A polar bear is a lot less endangered than a grizzly bear, and could better defend itself against the other. Unless you are on snow or ice, the grizzly usually wins. Either way, one of them would be dead.
They’ll both die if they fight each other because polar bears are unable to cope with their dry habitats and grizzlies won’t be able to survive in the cold (polar bears hibernate).
Polar bears have evolved for Arctic climates so they’re built for surviving under intense cold from very snowy environments. But they’re not well adapted to hot or humid environments which are more likely on land–that’s why when global warming destroys their homes then a lot of them also end up dying. Grizzlies on the other hand can survive in more different types of habitats and climates but they’re not as well built as polar bears to deal with the cold.
