Things like healthcare are minor hurdles at the end of the day, when you have a giant carrot dangling in front of your face. Things tend to happen. To be honest, I foresee Obamacare morphing in to nationalized healthcare in the future anyway. We'll see if we get a Republican president next time, if he's able or willing to undo it. My instincts say "no." I think we were going in that direction one way or the other, and Obama is the scapegoat for what is now an unpopular program.
I think an economic and military union/entanglement are inevitable. In many ways, we already have it. I think a single currency, if the Euro experiment works out, is also an inevitability. Every time you sell something in to the US, or buy supplies from the US, you have to pay an exchange fee (or vice versa of course). That's too much money lost from the economy that doesn't really need to be.
I don't think you'll ever see Canada 100% run out of Washington, though. That's simply not necessary. Like I said earlier, I foresee something like the United Kingdom's arrangement, where you have your parliament and we have our government, but there is some kind of umbrella representing both parties as well.