i concur with the person who suggested you contact your outfitter and ask his opinion (as a non resident you must have a guide). trailer loads of brown/coastal griz have been killed with 30-06 and 300 win mag. your guide will have the artillery, so let him hump the weight. take a rifle that you are confident with and shoot well. the likelihood of you being charged or attacked are ever so slight. i lived/hunted alaska for many years, using either a 270 win or 30-06. a 30-06 with partitions (either 180 or 200) will handle the bears mentioned and you'll probably shoot it better that the cannons. of course, if you just "want" a big rifle for this hunt you might as well get a 375. but make no mistake, a 30-06 or 300 win mag with a well-constructed bullet will cleanly kill these bears.