Aggression - The grizzly is a carnivorous animal and that utilizes far more aggression than that of a vegetarian animal who just has to climb up a tree to eat a banana or tear grasses out of the ground.
Speed - a grizzly bear has a maximum running speed 56 km/h. Source cited was http://www.speedofanimals.com/an...
That speed means that the grizzly bear can hunt down that gorilla and pound him before the stupid gorilla even knew what hit him. Source cited: my imagination.
Agility - Grizzly bear is so agile that he makes SCRUM masters cry.
Natural weapons - Freaking claws
In conclusion grizzly bear will slap the fuck outta silverback gorilla