Question: On what date did three British colonies unionized to form the federal dominion of Canada?
About the article "Canada", section "Abstract".

Candidate passages:
Canadian Confederation () was the process by which the federal Dominion of Canada was formed on July 1, 1867.
On that day, three British colonies became four provinces of the new dominion.
The existing United Province of Canada was divided into the new provinces of Ontario and Quebec, and two other colonies, New Brunswick and Nova Scotia, also became provinces of the new Dominion of Canada. 
The territorial evolution of Canada began when, on 1 July 1867, three colonies of British North America were united into the federal Dominion of Canada through Confederation.
One of these colonies split into two new provinces, and three other colonies joined later.
As a British colonial possession, Canada continued to accrete new provinces and territories and evolved over decades into an independent nation.
Before being part of British North America, the constituents of the Dominion of Canada were part of the colonies of Canada and Acadia in New France, which were gradually ceded to Great Britain and later the United Kingdom after defeat in several wars.
The French influence lived on, as the French language was common in the initial provinces of Canada, and remains one of the two official languages of the country.
The central expanse of Canada was originally settled by the Hudson's Bay Company of the Kingdom of England, which had a royal monopoly over trade in the region; Rupert's Land was named after the company's first director, Prince Rupert of the Rhine.
The North West Company later moved into a large portion of the region, and competition and minor hostilities between the two companies forced their merger.
What was to become the Colony of British Columbia was claimed as part of New Spain and Russian America, until 1793 and 1825 respectively, and was for a time shared with the United States as what was known to Americans as the Oregon Country, until in 1846 the border was extended west from the Rockies to the Pacific along the 49th Parallel.
Since it was formed, Canada's external borders have changed seven times, and it has grown from four provinces at Confederation to ten provinces and three territories.
It has only lost significant territory in the border dispute with the Dominion of Newfoundland over Labrador, which later joined Canada as the 10th province. 
The term "Dominion" is employed in the Constitution Act, 1867 (originally the British North America Act, 1867), and describes the resulting political union.
Specifically, the preamble of the act states: "Whereas the Provinces of Canada, Nova Scotia, and New Brunswick have expressed their Desire to be federally united into One Dominion under the Crown of the United Kingdom of Great Britain and Ireland, with a Constitution similar in Principle to that of the United Kingdom..." Furthermore, Sections 3 and 4 indicate that the provinces "shall form and be One Dominion under the Name of Canada; and on and after that Day those Three Provinces shall form and be One Dominion under that Name accordingly".
Usage of the phrase "Dominion of Canada" was employed as the country's name after 1867, predating the general use of the term "dominion" as applied to the other autonomous regions of the British Empire after 1907.
The phrase "Dominion of Canada" does not appear in the 1867 act nor in the Constitution Act, 1982, but does appear in the Constitution Act, 1871, other contemporaneous texts, and subsequent bills.
References to the "Dominion of Canada" in later acts, such as the Statute of Westminster, do not clarify the point because all nouns were formally capitalised in British legislative style.
Indeed, in the original text of the Constitution Act, 1867, "One" and "Name" were also capitalised.
Frank Scott theorised that Canada's status as a Dominion ended with the Canadian parliament's declaration of war on Germany on 9 September 1939.
From the 1950s, the federal government began to phase out the use of "Dominion", which had been used largely as a synonym of "federal" or "national" such as "Dominion building" for a post office, "Dominion-provincial relations", and so on.
The last major change was renaming the national holiday from Dominion Day to Canada Day in 1982.
Official bilingualism laws also contributed to the disuse of "dominion", as it has no acceptable equivalent in French.
While the term may be found in older official documents, and the Dominion Carillonneur still tolls at Parliament Hill, it is now hardly used to distinguish the federal government from the provinces or (historically) Canada before and after 1867.
Nonetheless, the federal government continues to produce publications and educational materials that specify the currency of these official titles.
Defenders of the title "Dominion"—including monarchists who see signs of creeping republicanism in Canada—take comfort in the fact that the Constitution Act, 1982 does not mention and therefore does not remove the title, and that a constitutional amendment is required to change it.
Canada Day () is the national day of Canada, a federal statutory holiday celebrating the anniversary of the July 1, 1867, enactment of the British North America Act, 1867 (today called the Constitution Act, 1867), which united three colonies into a single country called "Canada" within the British Empire.
Originally called "Dominion Day" (), the holiday was renamed in 1982, the year the Canada Act was passed.
Canada Day observances take place throughout Canada as well as among Canadians internationally. 
At common law, a person born within Her Majesty's dominions became a British subject at birth.
The various colonies of the British Empire passed their own laws determining how naturalization as a subject could take place, as well as what status aliens possessed, within their respective jurisdictions.
Upon the passage of the "Constitution Act, 1867", the Parliament of Canada was given authority over "Naturalization and Aliens", by virtue of section 91(25).
The "Aliens and Naturalization Act, 1868" was the first federal Act to be passed, and it provided that persons that had been previously naturalized in any part of the Dominion possessed the same status as anyone naturalized under that Act.
In addition:  Aliens could apply for naturalization after three years' residence in Canada.
Alien-born women became naturalized by marriage to a natural-born subject or to a husband naturalized under the Act.
The laws in Nova Scotia and the former Province of Canada that allowed aliens to hold property were kept in force.
The 1868 Act was replaced by the "Naturalization and Aliens Act, 1881", which came into force on 4 July 1883.
It made the rules allowing aliens to hold property uniform throughout the Dominion, and otherwise standardized the law along the same lines as the "Naturalization Act 1870" of the United Kingdom.