Let’s make it efficient and just have a population swap.
I thought we did that back in the 1890's?
As for the Czech and Slovakia, sure why not? As long as they don't bring any of their communists with them. And Since this thread is about a Latin American, I say we add Chile as well (although since they are a 1st world country with a 1st world economy, unlike so many other south american nations, they are actually solvent, I am not sure they would want to be involved with our S.S. system)
We could annex Poland. Then ths United States would border Russia on two sides.