England is going to have a lot more problems to deal with in Europe.I honestly can't see how the Union wins this war. They had a tough enough time OTL with just the CSA. CSA + Britain? It's only a matter of time. Plus the CSA is even stronger in TTL since the absence of a blockade means they can freely import any supplies they need. Union is doomed imo.
The war with the United States could be eclipsed by far more serious problems closer to home.