If we were ever going to divvy up the United States then we should do it in a manner that more closely resembles the
The Nine Nations concept, not a pure Northern/Southern United States divide, with the difference that the surrounding nations would divide the "Empty Quarter" between themselves, and allowing for the possibility of real native nations.
Not that a favor any separation at all, rather I would like to see Canada become part of the Union, and potentially a post-Castro Cuba... and not via coercion. I think the Canadians will figure out, sooner or later, that it just doesn't make sense for them to maintain the current state of affairs. We are practically one nation now anyway.