Impossible to say without looking like an idiot (apparently, it's not a concern for some here).
a) if annexation happened overnight, it probably wouldn't go down to well. Despite having a culture identical to Americans, Anglo-Canadians don't want to be annexed and would not be too pleased about such a thing happening. I won't even go into Quebec's issues.
b) overnight or not, the parties would be forced to adapt and accommodate themselves. Canada will never vote for a party as extreme as the GOP is in its present state, so unless the GOP fancies playing the role of the eternal small opposition, it will be forced to adapt. I can't state the importance of this point enough.
c) vastly different issues would be in play and would affect voting patterns considerably
But obviously it's much more fun to make stupid assumptions and draw nice useless maps!
