Both Polar bears and brown bears have circumpolar ranges.
Brown bears have viable populations in Europe and Asia. Polar bears exist all around the Arctic.
It is difficult to find a good count of polar bears. It appears the "experts" don't want to release the numbers they have.
The famous researcher Susan Crockford shows the idea is simply false.
Even in Iowa we get the occasional black bear sighting from Minnesota or Missouri but no established population.