Apparently planning is already underway for superhighways from Mexico through Texas and up into Canada in preparation for the North American Union. I wouldn't be surprised to see a globalized government by 2020 if this is indeed the pace at which this is going.
For the conspiracy-theory interested folk in the crowd, I recommend looking into the Bilderberg Group, they're supposedly behind all of this globalization.
I must be getting old because I think any further integration will be disastrous for Canada. We have health care, slightly more sensible parliamentary government, haven't dug ourselves into a hole on borrowed credit, and one of the best electoral systems in the world (despite its flaws). I'm so moving if the US, Mexico, and Canada ever join 
Not going to happen anytime soon. We'll probably see integrated defense and definite strides toward integrated border security in the next couple decades. We might even see a common currency. However, you aren't going to see the same sort of political union in North America that has cropped up in Europe. You have three nations that are extremely different politically and socially. Europe, in contrast, had become remarkably similar (and let's not forget that the EU took 50 years following a major world war to assemble; the idea to link Europe's economies had been tried and failed once before that).
Ultimately, the conspiracy nuts are exactly that - nuts. The SPP, which they target as a sign of the apocalypse quite regularly, is an attempt to bring widely different strategies for control over border security and immigration into some kind of standard - a good step in the right direction, because it moderates out the bad policies. As for the "Amero" - hell will freeze (or the markets will fail entirely) before the US gives up its dollar. Canadian business relies on a separate fluctuating currency for trade with the US, so we won't be giving ours up anytime soon either - not, at least, without a major overhaul of NAFTA. Mexico wouldn't gain much from an integrated currency either - tourism would flop as prices came into line. Mexico is a tourist destination because its cheap. Lose the economic advantage and people will go elsewhere.
Truth be told, given a major overhaul of NAFTA an integrated currency across the three countries would be a brilliant move in the long run (particularly for the USA) because their President would no longer be able to hammer it through foreign policy. That, and it could compete directly with the Euro. Right now the bet is on what's going to become the predominant trading currency to replace the US Dollar worldwide, and smart money is on China or Europe. Personally, I'd bet on the Euro given the geopolitical stability of the region. An integrated dollar in North America could change that.
The problem with conspiracy theories is they assume there's some master planner behind it all, and they totally ignore the forces of social change (ironic, considering most conspiracy-theories are born out of 1960s and 1970s era ideology which was founded on social change). Business interests aside, the populaces of the three North American countries are not prepared for the kind of integration the conspiracy folks are predicting, nor is the social infrastructure. And until you can begin altering those forces, you don't have a hope in hell of a meaningful political change.
