Fear of MEXICO being brought into some form of union with the US outside of trade and a bit of security cooperation (which would be a good thing for a number of reasons IMHO)is at this time over the top. There will be no EU style arrangement on this Continent. There is no advantage to it for all the players. The EU succeeded because every country there basically sucked, so it "helped" everyone.
You think the EU is a success?
At what?