I think that the gorilla would probably win because it is most likely smarter and could probably use a weapon. It would have to be quick and strategic though as the grizzly is very strong. Since grizzlys tend to stand up and growl, they become vulnerable to a quick move. The gorilla would have to use this quick time frame to make a stunning move and then finish the bear off. But if he failed and got to close, the bear would obviously have him for breakfast, haha.
I honestly think that that jaguar from that youtube video keranu posted could probably take out both grizzly and gorilla. The jaguar has both intelligence and insane speed/reflexes. But the jaguar ain't a contender, haha.