What if we were forced to stick with the Democrats and Republicans?
Democrats would win in a landslide.
Assuming every other country in the world joined as new states, the Republicans would only win the US states they do now, the very wealthy reactionary Arab kingdoms, and maybe a couple of sub-Saharan African countries by getting the anti-gay crowd all riled up. And possibly Poland.
I don't know about that, Canada and Australia at the very least would be competitive. Their conservative parties are currently in control of the parliaments, and the people who support those parties would probably identify more easily with the Republican party than the Democratic party.