Amero. Economic nationalism is 20th-century.
I'd have no real objections to a joint US-Canadian currency in theory. The problem is, US deficit spending is so out of control any new currency would succumb to inflation in no time. Not to mention the issue of existing debt as a result of said spending (which is reaching critical levels)...
Not really, several European nations, ahem France ahem, have deficits above the level proscribed by the European Comission but the Euro has yet to collapse in an orgy of inflation and declining purchasing power. Nor has this ever happened in the US, we've never had a major spiral of inflation we've had massive deflation, as occured during the start of the Great Depression, but never any massive inflation even during the stagflation years of 1970s.
Well I wouldn't go that far. The Dollar and the Euro will still remain the top two reserve currencies in the world at large for at least the next half century so I don't think you have to be worried about American currency devaluing substantially and, if it does, you probably have some other more pressing concerns to deal with, such as a global great depression, a massive war, or a complete destruction of the western world. Although I suspect the Euro to become more sluggish in the near term, as America slips into a second recession in this decade Europe will probably, inevitably, be bitten by the bug of economic downturn. What we are seeing now is that the American economy is heading towards recession, most likely, while the effects of this recession haven't fully caught up with the rest of the world yet.
If you are truely worried about this, though, I would suggest a Swiss bank account with your account held in a common reserve so that you can transfer the money from American dollars, to British Pounds, Euros, or Swiss Francs, or between any of those currencies, at a whim, and on the back of market forces too to earn a good amount. Also I believe some also allow you to convert your assets into gold if you are truely concerned with currency devaluation.