Others for Toronto:
Union Station
Constructed between 1914 and 1920, and opened in 1927, Union Station is the busiest station in Canada and in North America outside of Mexico City & New York City. It's also home to one of the first stations of Toronto's and Canada's first subway (Line 1), and is the best example of Beaux-Arts Architecture in the city (opinion).
https://www.flickr.com/photos/441244...N01/3154249588 (Duncan Rawlinson)
Casa Loma
Construction on the largest residence in Canada started in 1911 and completed in 1914, designed by E.J. Lennox a prominent Toronto Architect who also designed buildings such as Old City Hall, Beard Building (Dem. 1930's), The King Edward Hotel, and the Toronto Generating Station in Niagara Falls. It's a Gothic Revival style building and was home to Henry Pallat (Who commissioned Lennox to design the "house"). Pallat left the residence in 1923 and ownership went to the city almost immediately and was left vacant. The property is owned by the City of Toronto and protected under the Ontario Heritage Act, and is currently leased by Liberty Entertainment Group which hosts several kinds of venues at the castle.
casaloma.ca
Skydome (Rogers Centre)
I refuse to call it by its official name even though I can't remember the time it wasn;t called teh Rogers Centre but it was built in 1988-1989 on former CN/CP Rail lands and was the first solid retractable roofed stadium on Earth. It's iconic because of this factor and its size and its proximity to Toronto Iconic Building #1 (and arguably Canada's most iconic as well but that's debatable) the CN Tower. It's in nearly every postcard of the city since 1988 because of the CN Tower's status and became an icon of its own in the process.
Editing further later