Who would win in a fight between a bull and a polar bear?

That all depends on the bull itself. Not all bulls have horns, and not all bulls weigh 2000 lbs. It also depends on the breed of the bull and its temperament. Normally bulls, as prey animals, choose to flee from a predator like a polar bear rather than stand and fight, and a polar bear wouldn't know what to make of a bull in the first place, since they don't actively hunt cattle, but instead seals and walruses, and maybe the occasional caribou and muskox.

Maybe if the bull was a little Dexter the polar bear might win. But if it was against a 2200 lb Spanish Fighting Bull the polar bear may loose. The polar bear may even lose if it's against a hot-tempered Chianina bull. So who knows?