1. USA
2. Soviet Union (had Stalin actually been prepared for the attack, even the purged army would have ended the war by 1943 at the latest, likely 1942)
3. British Empire
4. Germany (it was rapidly expanding, but it won so much merely because of great military strategy and enemy incompetence)
5. Japan
6. France (I think they fall just behind France)
7. Italy
8. Poland (wasn't too bad, just used wrong strategies and too much cavalry)
9. Getting hard from here... I'd say a South American country and either another SA or maybe Yugoslavia.
China - not a chance. It may have had a large army, but it was extremely corrupt and poor quality. Thanks to Soviet and American aid, China merely managed not to be completely overrun by the time the US could do anything about it. Warlordism was a big problem.
Czechoslovakia - not in 1939, when the Munich treaty tore them apart. Especially in late 1939, when they no longer existed, of course.
Canada - they weren't really strong, as they had no interest in expansionism. They merely helped out a bit and that was it.
Netherlands - I argued a 10th place for it for 1914, and while I uphold it was a contender back then, definitely not this time. Netherlands just gave up on army improvement by this point.
Axis lapdogs - no chance. Especially not Hungary, who actually employed bicycle divisions. Finland neither, they held out so well because the USSR underestimated them and because Karelia is a natural fortress anyway. (Plus Mannerheim and all that.)