weird political question involving imperialist views?

There's a few problems:

Both:

Young People don't want the drinking age to go up to 21.

Canada:

People Don't Want Health Care Reprivatized.

People will be worried about getting dragged into wars.

Mexico:

Everyone speaks spanish.

National history includes having half the country taken in a war with the United States. A "union" would be perceived as the rest of the country being taken over.

And for your last question "no" I do not think this would make us all more safer and prosperous. Even if the three different systems would hypothetically compromise you know it would be lead by the United States. That would mean even more deregulation and commercialization in Canada, extending the control of multinational companies. Mexico might marginally benefit as some labor laws are more rigorous in the US. In the end even if this union continued for some time it could easily degenerate into a Yugoslavia situation.

The bigger need is for a system of world federalism. Overcentralization must, of course, be avoided. Big government isn't the solution. But world federal government, based on a free market and free trade, is ultimately the next stage in our development on this planet.

Not for Canada & Mexico at the moment.