You wouldn't see one state/province going to war
against one another, would you?
Actually you would. There are plenty of historic and recent conflicts between different regions of the same state. I can think of quite a major one in the US alone.
So, what do you think the reasons are that there is no unification movement?
Maybe since there isn't a problem with wars between the US and Canada, people don't really see the necessity with unification of the two nations to foster peace and understanding between the two of you.
Also because the Canadians doesn't need the US to run a well functioning country and don't feel the need to share power over their own lives and their own laws with a bunch of American hillbillies who wish to impose their cultural values and ideas on them. You know the same reason secession movements are much more popular in the world in general.