Go.
Edit: it has came across me that the US will annex Canada in 50 years, all arguments are meaningless.
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Historically the United States has failed in 2 and 1/2 invasions of Canada. Once during the American Revolution. Then the failed invasion during the war of 1812. Finally the failed Fenian raids after the Civil war. On Americas side. Today we have nuclear weapons to protect Canada and Canada is a major purchaser of American export weapons.