I dont see how Canada which is where I live is Americanized. We come from the same cultures and that live the same life style. Its not we are Americanized, we could say Americans are Canadianized.
And why do Americans have to emigrate to Canada, I could see them entering Canad and them being there but there would also be Canadians.
1. In the FO Universe, Canada was taken over by the US, and most likely Americanized by the new American puppet regime. (If there was one at all, but it's most likely there was one, seeing how our own world power systems operate to put people in power that would agree with their ethics, and code of doing things.)
2. If you read a note in FO3, it says that said person(s) were not granted the chance to participate in a Vault, and so are given the hint to possibly move up to Canada instead of staying in the US, incase of thermonuclear war. And I'm sure that with the problem's the US was having, Americans probably would have moved up into what was then Annexed Canada, for a more livable, and hopefully, less chaotic place since American people (keeping with the 50s mindset), were confident in the US troops there, to keep the peace, etc.
3. When I visited BC Canada, I saw more of the youth and such having a more American tone, since just across the water, America was right there. (And this was before you needed a passport to get across the Canadian/American border, etc.) When I went farther up into BC, I saw they had less of an Americanized sense of style or what have you, so I'm not trying to say that all of Canada, or even all of BC has been Americanized, just that some of where I visited, was. It would probably be even more evident that Canada in the FO Universe was Americanized, though of course there would also be resistance to Americanization. But keeping in the 1950s American mindset that FO is, I'm sure that Canada would have met it's doom with some form of Americanization all across the country that the US controlled. It might not have been much, but I'm sure there was some.