>>1988025Grizzly x polar bear is viable, has been documented, but some populations of grizzly bear are more closely related to polar bears than other grizzly bears anyway.
Intergeneric offspring in tetrapods are on the rare side, though they do happen. But panda hybrids with any other ursid would be extremely rare even in captivity, if at all possible. Species in Ursus are fair game though. Might be possible, but it's very unlikely.