Hmm... My Black Bear squared out just over 6'. Just about 300 pounds. Not huge. Above average for Washington State. 25yds with 30-06. quartering toward me. Left fore leg, and both lungs. Missed the heart. If it wasn't for the windfall between the two of us, he'd have hurt me. He still ran another 75yds. I still had to put two rounds from my 44mag in him to put him down. I hand-gun hunt, 44mag as a minimum, or just once in while with 8" .357mag Dan Wesson.
Just remember, in most cases, those Bears are more afraid of you than you are them. (Park Bears not counted), (Sow with cubs not considered.) Most often if you just make noise, stand and wave your arms, they'll turn tail and run.
Pepper spray is a good idea. If a person has to ask if the .45acp is big enough, they're not an experienced hunter, and probably not comfortable with shooting a bruin at close range. Don't even consider the .357sig or .400corbon. So, I'd say the 44mag with lots of practice until he's comfortable and confident.
-Steve