Regarding two republics vying for additional territories in the west, you are probably correct.
Had the South won her independence there’s little doubt the Confederacy and the Union would have remained enemies. In order to hurt the South’s economic output, there’s no doubt the Union would have encouraged slaves to come north. That doesn’t mean they wouldn’t have funneled them up to Canada or ferried them to Liberia. It also doesn’t mean that the Union wouldn’t have created a colony for freed slaves somewhere in the plains. They had already done this with Indians, why not black slaves as well?