For the big companies it is an obvious great idea. The US gets Canadia resources and Mexican labor. And as a side benefit, when such deals are crafted enivronmental and labor laws are usually mandated down to the lowest level found in any of the countries.
It has been obvious since NAFTA that there is a certain buisness circle that wants this to happen. And they are people used to manipulating big governments over time to slowly make what they want the defacto law no matter what the written law actually says.
Jay