If I had to carry a .45 ACP in bear country I think I would polish up the feed ramp and cast up some 452423 Lyman 238 grain bullets ahead of a stiff load of Blue Dot. This bullet was designed by Elmer Keith for the 45 auto. I have used it in a 25 and a 625 Smith and it is very accurate and a lot better choice than a ball load.
The OP specifically asked about a 45 ACP ant in my humble opinion that's the best choice. I have never hunted in grizz country ,but have fished ,and like I told my brother in law when he laughed at me for carrying my 44 mag. It beats the he!! out of trying to whip them to death with a fly rod.