(male) Grizzly Bear: 600#
(male) Hippo: 3500#
The Hippo has powerful jaws and exceptional quickness. "On the National Geographic Channel television program, "Dangerous Encounters with Brady Barr", Dr. Brady Barr measured the bite pressure of an adult female hippo at 1,821 lb (826 kg); Barr also attempted to measure the bite pressure of an adult male hippo, but had to abandon the attempt due to the male's aggressiveness."
I think the Grizzly would try to circle around the Hippo to attack its more vulnerable flank, but fail. The Hippo could just turn in place.
The Hippo eventually kills the Grizzly by either trampling it underfoot, maiming it with a vicious chomp, or squashing it with a Sumo-style bellyflop.
This is all considering a dry land confrontation. In even 1-2' of water, the Grizzly would be practically defenseless.