No way. I don't understand this obsession with moving toward a world government. I'm all for cooperation between countries, and frankly the US needs to show more respect to our Latin American neighbors than we do, but concentrating the government's power further from the people will only make it less responsive to their needs.
I've always enjoyed the thought of humans in the future as a space-faring civilization that effectively functions as one country, possibly a federal republic. I think the further we want to advance as a species is dependent on how closely we can work together, instead of constantly fighting and competing with each other.
Though as it stands
right now, given the current state of some of our neighbors south of the border, I have little interest in an "American Union".