First off I'm 19, and I'm majoring in International Politics and Economics right now, just so you don't think I'm 15, and I have already voted for Obama in Washington's caucus. Regardless reforming NAFTA would be beneficial to Canada and Mexico as well as the US, Obama has publicly said that he is going to work with both nations leaders to fix the problems in NAFTA and support all of our economies. The US has no reason to devalue the Canadian Dollar, and not matter what anyone does the American Dollar isn't going to get back to its old strength anytime soon.
Also your idea that restricting trade would hurt Canada and Mexico's economies is unfounded, many Mexicans support restricting agricultural trade with the US that was opened up by NAFTA because it has hurt, not helped, Mexican farmers. The same in Canada a stronger Canadian Dollar will cause labor to be cheaper south of the border in the US where I bet many Canadian manufacturing jobs could head if NAFTA isn't reformed.