I think that quite many who suggested shotgun for a bear thought about attacking bear and close ranges. I used to use my 9,3x62 battue rifle in brownbear (there are only brownies in finland) hunting and it would be good choice in any bear situations.
If there was situation that bear attacks on you at 30 mph and you get your first shot at 20 yds could you really stop that attack before that bear reach you?