The silverback gorilla is 7 times stronger than the average adult man, 6 feet tall and 360 lbs pure muscle. It also has knige sharp teeth the size of a butterknife.
The brown bear is around 750 lbs, much stronger than the gorilla with more claws and teeth but much less agile and much slower.
To clarify:
By brown bear i mean a big male grizzly bear. A kodiak bear would almost definetly win but this is just a grizzly.
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Considering bears have enough thickness to survive multiple gunshots, and have the power to rip weaker animals (like humans) apart easily, they'd be hard to take down with claws and teeth. However, the fact that gorillas are a fairly intelligent species with opposable thumbs, fast, and extremely strong, gorillas would be a good fight. I'd probably take the bear though. If it got a good hold on the gorilla it could tear it to pieces. Plus being twice the weight, and with how much natural defense they have.