If you really think it's all about trade and commerce, there's a famous bridge in NYC that's for sale.
Well its is about trade and economic prosepects on both sides of the border. This is a simple fact. There will be no political merging of the three countries. Such an agreement would never never pass the senate. That is likely as to happen as the congress repealing univeral suffurage. Furthermore for many of Mexico's problems they do have a strong nationalistic streak. Theyu would never vote to be engulfed by the USA. Further, would Canada give up all their socialist goodies to merge? I think not.
This is a effort to lower trade barriers that will benifit us all