Especially in the east part of the continent. If you wander the street of any of the 4 major Canadian cities on the east coast, Toronto, Ottawa, Montreal and Quebec City, you could easily see medieval gothic style architecture everywhere. Just look at White House and the Capitol vs Canadian Parlement, Old US universities like Harvard, Princeton vs Old Canadian universities like McGill, U of Toronto…you can easily see the difference in architecture style. Is there any historical context that could explain this deviation in building styles across boarder?
My hypothesis is that Canada established it's institutions later than the US and thus the styles in vogue were different.
It's generally referred to as Gothic Revival and it was the style in fashion around the time of Confederation (1867). Thus many of the new institutions, including parliament and most of Ottawa, were built to this style and followed other broadly Victorian influences.
Most of the American institutions were built up almost a century earlier and used the Neoclassical style in vogue at the time. The Washington Capitol was completed in 1800 while the Parliament was completed in 1876.
I would say those initial buildings may have set the tone of what was expected of state buildings as both styles are near ubiquitous with each country's institutes.
It became a sort of signature style for a lot of Canadian buildings built during the Victorian period. It's more associated with protestant anglophones though. The only exception is several Catholic churches.
Montreal and Quebec City contain lots of exceptions to that trend. The National Assembly for instance was built in a Second Empire style rather than Gothic Revival. Much of the housing in French neighborhoods employ more traditional french building styles, something that was a tradition since the conquest. Anglophones even prefered french styles in the early days of British rule, but by confederation housing became very distinctly Victorian in English neighborhoods. Montreal, Toronto and Ottawa are full of these types of houses. Most of the English houses I know of in Québec City are around La Grande Allée.
I would say it's really of sign of how the founders of the dominion really wanted to distinguish themselves from the US while calling back to Britain and more widely Europe.
By the 20th century you start seeing more overlaps with American architectural trends. That could also be a sign of that shifting affinity as the 20th century slowly marked the end of Britain's influence on Canada.
Gothic architecture was used nevertheless for a long time in Canada. Longer than most other countries. The Westmount City Hall is a good example of a weird medieval castle looking building that was constructed in the 1920s... Again a civic building. A bunch of government buildings in Ottawa were built in that style with the copper roofs that went green way into the 20th century. I guess it was just iconic.