Is a polar bear stronger than a grizzly bear?

Is a polar bear stronger than a grizzly bear?

However, grizzly bears are tougher than polar bears as they possess stronger and longer claws and an elongated skull with sharp and long canines that can completely separate the flesh from bone.

Do polar bears fight other bears?

Aggression occurs between males during the breeding season and when males attempt to steal food caught by other polar bears. Play fighting has been observed between aggregating subadult and adult male polar bears