Okay hopefully this won't get too political and annoy any mods.
Simply put while Canada is not as french as a lot of people tend to think, it has some VERY strong socialist leanings and maintains strong relations with a lot of socialist countries. In simple terms socialism being the evolution of communism. Communism being the idea that everything belongs to everyone, and socialism being the idea that everything belongs to the goverment which distributes it fairly to the people based on need. Nobody follows these ideas in perfect "unmodified" form, nor am I criticising. This is not intended to be a political rant as much as it is to point this out.
Much like my post about Europe (which I hope is still up) I'd point out that a conflict between the US and China/Russia is ultimatly one about democracy/capitolism type thought vs. communist/socialst type thought on a practical level. Nationalism of course also enters into it on all sides, but when looking at the conflict going down nations are going to pick a side based on belief. Members of a European Commonwealth who are trading on all sides are probably not going to agree with which side to take, and thus everyone is going to split up. Canada which while very similar to the US in a practical sense does have an idealogy that has oftentimes had them siding with nations like France against the US.
Depending on how things played out, and IF Canada believed that China was going to win the war, they might very well have sided with the eastern powers. Given the resource wars it is also unknown how much bad blood might exist between the US and Canada over trade, or what ties might exist with Europe and other powers if for example they were buying their gas from them, while the US somehow became self sufficient in that regard, or developed technology where it didn't back Canada based on it's needs.
All of this is of course supposition based on possibilities of how the game information could have transpired, rather than a direct commentary on real politics (for those who might object I will point out that the Democracy/Communist conflict already exists in Fallout 3 via things like a propaganda station, so I don't consider talking about this to be excessively political in the context of the game).
Canada has a decent military, granted not as big and bad a one as the US right now, but if they started building up, or hosting troops from overseas as such a conflict started building... well... yeah we might attack/annex it.
Due to the need to avoid RL politics I won't get into Quebec.
>>>----Therumancer--->