I tried to find an answer to that - it appears that despite what we tend to think, Mexico is "richer" in terms of GDP than many other countries. I know - get out of town! - but it seems to be so.
Mexico average is $14,400; Poland is $17,800. And without trying to figure exactly who is a member of the EU - to answer your question, I tend to think not.
As far as a NAU - who really wants it? Mexico and some of the South American or Central American countries might be sort of interested, but realizing the tensions between them...no, they do not want to unite, per se. South America is SO fragmented and diverse = they might wish to, but they simply cannot.
And America will not do it with Mexico and Canada likely would not do it with us. Canada is a headache to the people who try to govern there, let alone join with the USA and/or Mexico.
It is very good question, to be sure, but it is just not workable, as the EU is finding out.