I mean, similar is not identical. They are primarily English-speaking, White, capitalist, democratic, top 30 in GDP per capita, founded by European settlers, both spent over 100 years as a British colony, and share the longest land border of any two countries in the world, right?

I've seen a lot of Americans mistaken for Canadians abroad, and a lot of Canadians mistaken for Americans. I've yet to see either mistaken for Mexicans.