Polar Bear. The battlefield is totally unsuitable for the gorilla.
Even "a little bit of snow" is unsettling enough for an animal that lives in the fucking jungle.
Maybe mountain gorillas just have a chance at not shivering enough to climb a tree and call it quits. Since most polar bears have never seen a tree in their whole lives, I doubt they be able to climb it.
Now I'm too stoned to wiki the details, but I'm sure you people will find it more fun to decide the winner through random opinions rather than facts anyway