Question: What era was the well known buliding on the border of United States and Canada declared a heritage building by both?

Context paragraphs:
Vigan: Located on the western coast of the large island of Luzon, facing the South China Sea, is a UNESCO World Heritage Site in that it is one of the few towns left in the Philippines whose old structures have mostly remained intact, and it is well known for its cobblestone streets and a unique architecture of the Philippine colonial era which fuses Native Philippine and Oriental building designs and construction, with colonial Spanish architecture.  Former Philippine president Elpidio Quirino, the sixth President of the Philippines, was born in Vigan, at the former location of the Provincial Jail (his father was a warden); he resided in the Syquia Mansion.

Grade II* listed war memorials in England: There are 61 Grade II* listed war memorials in England, out of over 2,000 listed war memorials.  In the United Kingdom, a listed building is a building or structure of special historical or architectural importance; listing offers the building legal protection against demolition or modification, which requires permission from the local planning authority.  Listed buildings are divided into three categories—grade I, grade II*, and grade II—which reflect the relative significance of the structure and may be a factor in planning decisions.  Grade I is the most significant and accounts for 2.5% of listed buildings, while grade II accounts for 92%.  Grade II* is the intermediate grade accounting for the remaining 5.5%; it is reserved for "particularly important buildings of more than special interest".  A war memorial listed at grade II* may be of particular artistic interest or accomplishment, of a highly unusual design, or of significant historical interest below that required for grade I.  It is explicitly unnecessary for the architect or sculptor to be well known in order for a memorial to be listed at grade II*.  As part of the commemorations of the centenary of the First World War, Historic England—the government body responsible for listing in England—is running a project with the aim of significantly increasing the number of war memorials on the National Heritage List for England.

Haskell Free Library and Opera House: The Haskell Free Library and Opera House (French: Bibliothèque et salle d'opéra Haskell) is a neoclassical building that straddles the international border in Rock Island (now part of Stanstead), Quebec and Derby Line, Vermont.  The Opera House opened on June 7, 1904, and was deliberately built on the border between Canada and the United States.  It was declared a heritage building by both countries in the 1970s.

Line house: A line house is a building deliberately located so that an international boundary passes through it.  The term is perhaps more frequently used in reference to the boundary between New England and eastern Canada than to other places.  The most well known such building on the boundary between the United States and Canada is the Haskell Free Library and Opera House in Stanstead, Quebec and Derby Line, Vermont.  The border is marked on the floor in a reading room and an auditorium.  A number of single-family residences and some industrial buildings straddle the boundary in those two towns.

Churubusco–Franklin Centre Border Crossing: Churubusco-Franklin Centre is a border crossing connecting Franklin Centre, Quebec to Churubusco, New York on the Canada–US border.  In an unusual lack of coordination between the two countries, the United States committed to building a new $6.8 Million border inspection station at Churubusco, at the same time Canada committed to closing its Franklin Centre border station.  The result is an apparent permanent condition where travelers may enter the US from Canada via southbound Quebec Route 209 at this location, but they must return via another route instead of taking northbound New York State Route 189.

Canada–United States border: The Canada–United States border (French: "Frontière entre le Canada et les États-Unis"), officially known as the International Boundary, is the longest international border in the world between two countries.  It is shared between Canada and the United States, the second- and fourth-largest countries by area, respectively.  The terrestrial boundary (including portions of maritime boundaries in the Great Lakes, and on the Atlantic, Pacific, and Arctic coasts) is 8,891 km long, of which 2,475 km is Canada's border with Alaska.  Eight Canadian provinces and territories (Yukon, British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, and New Brunswick), and thirteen U.S. states (Alaska, Washington, Idaho, Montana, North Dakota, Minnesota, Michigan, Ohio, Pennsylvania, New York, Vermont, New Hampshire, and Maine) are located along the border.

Franklin Street Presbyterian Church and Parsonage: Franklin Street Presbyterian Church and Parsonage is a historic Presbyterian church located at 100 West Franklin Street at Cathedral Street, northwest corner in Baltimore, Maryland, United States.  The church is a rectangular Tudor Gothic building dedicated in 1847, with an addition in 1865.  The front features two 60 foot flanking octagonal towers are also crenelated and have louvered belfry openings and stained glass Gothic-arched windows.  The parsonage has walls of brick, heavy Tudor-Gothic window hoods, and battlements atop the roof and was built in 1857.  This church was incorporated in 1844 by a group of men from the First Presbyterian Church then located at the northwest corner of East Fayette Street and North Street (now Guilford Avenue) in downtown (later relocated in 1854 to West Madison Street and Park Avenue in Mount Vernon-Belvedere neighborhood after selling their previous third church building of 1790-95 to the Federal Government which built a U.S. Courthouse there [to 1889, replaced again 1932] dedicated in 1860 by President James Buchanan).  They felt the need for a new church in that fast-growing northern section of the city formerly "Howard's Woods" of Col. John Eager Howard's (Revolutionary War commander of the famed "Maryland Line" regiment of the Continental Army) country estate "Belvedere" (mansion located at intersection of North Calvert and East Chase Streets, razed 1875) where the Washington Monument was erected with its four surrounding park squares just two blocks from their new building.  Franklin Street Church was also located on "Cathedral Hill" in the southern part of the community bordering downtown and across the street from the old Baltimore Cathedral (Basilica of the National Shrine of the Assumption of the Blessed Virgin Mary) erected 1806-1821 and designed by Benjamin Latrobe.  Later in 1882-1886, philanthropist Enoch Pratt founded his central library for the new Enoch Pratt Free Library then facing West Mulberry Street at Cathedral, a block south which was replaced in 1931-33 by a new central library building encompassing the entire block and now directly across Franklin Street from the F.S.P.C.  In 1973, the two historic congregations reunited to form The First and Franklin Street Presbyterian Church and was centered at the First Church site on West Madison and Park.  The Franklin Street building was used by the merged congregation for a time and then sold to a fundamentalist independent Protestant congregation and later re-sold to the present "New Unity Church Ministries".  Across Cathedral Street to the northeast was the 1820s era Greek Revival home designed by Robert Mills (who also did the Washington Monument two blocks away) which later was occupied by the original Maryland Club, an exclusive Southern-leaning dining and leisure society of gentlemen, founded 1857 that was once threatened by Massachusetts Militia Gen. Benjamin F. Butler, U.S.A. when he occupied Baltimore at the beginning of the Civil War on May 13, 1861, and fortified Federal Hill with a Fort and cannons overlooking the harbor and city, "to put a shot into it" if he spied a reputed rebel flag flying or any discontent to declared martial law.  The Club later moved to North Charles and East Eager Streets in 1892 and mansion was later replaced by the former Central Building of the Young Men's Christian Association of Central Maryland (YMCA) which was closed in the 1980s and the building renovated as the Mount Vernon Hotel and Cafe.

Canada–United States relations: Relations between Canada and the United States of America historically have been extensive, given a shared border and ever-increasing close cultural, economical ties and similarities.  The shared historical and cultural heritage has resulted in one of the most stable and mutually beneficial international relationships in the world.  For both countries, the level of trade with the other is at the top of the annual combined import-export total.  Tourism and migration between the two nations have increased rapport, but border security was heightened after the terrorist attacks in the United States on September 11, 2001.  The U.S. is ten times larger in population and has the dominant cultural and economic influence in the world.  Starting with the American Revolution, when anti-American Loyalists fled to Canada, a vocal element in Canada has warned against US dominance or annexation.  The War of 1812 saw invasions across the border.  In 1815, the war ended with the border unchanged and demilitarized, as were the Great Lakes.  The British ceased aiding First Nation attacks on American territory, and the United States never again attempted to invade Canada.  Apart from minor raids, it has remained peaceful.

Hyder - Stewart Border Crossing: The Hyder - Stewart Border Crossing connects the communities of Hyder, Alaska and Stewart, British Columbia on the Canada–US border.  It can be reached by British Columbia Highway 37A from Stewart and International Street from Hyder.  There is no US border inspection station at this crossing, making it the only land border crossing where a person may legally enter the United States without reporting for inspection.  The US closed its border station, which was located in the same building as the Boundary Gift Shop, in the 1950s.  As a result, all flights leaving the Hyder Seaplane Base to other cities in Alaska are treated as international arrivals, and all passengers, including Hyder residents must be inspected by U.S. Customs and Border Protection officers.  Hyder is the easternmost community in Alaska.

Blackfoot Crossing: Blackfoot Crossing Historical Park is a complex of historic sites on the Siksika 146 Indian reserve in Alberta, Canada.  This crossing of the Bow River was traditionally a bison-hunting and gathering place for the Siksika people and their allies in the Blackfoot Confederacy.  Nearby are the remains of an ancient earthlodge village, believed to have been built by people from the Upper Mississippi valley in what is now the United States.  It is unique in being an example of a permanent village on the plains: an area associated with nomadic hunting.  The crossing became an important place in Canadian history when Treaty 7 was signed here between the native nations of what is now southern Alberta and the Canadian government on behalf of the Crown in 1877.  It was also here that Crowfoot, chief of the Siksika, is believed to have died and been buried.  As well, Poundmaker, a chief of the Cree who had been ceremonially adopted by Crowfoot in order to create peace between the Blackfoot and the Cree, was also buried here until being moved in 1967.  In 1925 the traditional gathering site and the treaty signing site were declared National Historic Sites of Canada by the federal government's Historic Sites and Monuments Board of Canada.  In 1972, the earthlodge village was also declared a national historic site.

Supporting paragraphs: Line house Haskell Free Library and Opera House
Answer: It was declared a heritage building by both countries in the 1970s.