Better what you have with you than what you would LIKE to have with you. .45 Super or heavy 10mm is more likely to be in the first category.Meh. I’m fine with 45 super out of a HK45 or USP for cats and black bears. 10mm isn’t enough in my book for brown bears anyway. 12ga slug ftw.
As for the second:
.45-70 Govt or maybe .444 Marlin in a Marlin 1895, .45-70 Govt. in a modern Winchester 1886 for the long arms. .44 Mag with good grips for a handgun. Those being options I have and am comfortable with, in addition to the 12g with slugs.