I visited Vincennes (Paris) and (west) Berlin Zoo many times during the 1980s when both collections had every species of bear:-
polar bear, brown bear, Asiatic black bear, American black bear, sloth bear, sun bear, spectacled bear and giant panda.
However, in Paris, two different bear species sometimes shared the same outdoor exhibit and were let outside on alternate days; consequently, it was necessary to visit on two consecutive days to be sure of seeing every species.
I think, also, that there was a time in the 1960s when London Zoo had every bear species simultaneously; certainly I saw every species there, many times, when I was a child during that decade. However, after all these years, I am not certain that I ever saw them all in the same visit. (During that period London Zoo had the famous giant panda "Chi-Chi" although, of course, in those days the giant panda was not considered to be a bear.)
Are there any zoos today that currently exhibit every bear species?