Question: What era was the well known buliding on the border of United States and Canada declared a heritage building by both?
Sentence (from "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.
Relevant evidence: No