Well, to copy the EU certainly would, but to have an economic union, with no trade barriers and eased restrictions on travel between countries would not. Or we could all become one country, retaining the US Constitution, which has the greatest protections for individual liberties, of the constitutions of the 3 countries. Mexico's constitution is a joke as far as individual rights and liberty goes... but at least they can follow theirs while trampling on the rights of the people, our government must violate ours to do so. Which of course, they do.
"Or we could all become one country"
I don't think we need to incorporate the culture of corruption that is Mexico.
Our type of constitution was designed for a moral people.