Gonna take each of these individually in reverse order:
I've been all over Alaska, after fishing seasons becoming a vagabond and wandering off. There seems to be various regional preferences, have come to the conclusion that there is no truly common alaska bear rifle. Coastal and West it's a ton of 338 win mags, know more that just a few guides with 375 hh. Up on the bering peninsula it was as equal a group of 30-06, 4570, 300 win and a smattering of bigger bore options. Towards interior and kennicott lots of the homesteaders had 4570. Southeast I never did see a certain specific preference, some villages it's all the same rifle as one guy buys a Hawkeye and liked it so the next year 20 bought the same... South central seems to be the land of a bit more moderation in cartridges. Probably because there are more people and less bear interactions, or hunters are focused more on other things and have a smaller chance of bear interaction.
Best I can say is "every guide used to have a 375 and every hunter used to have a 300 win". Doesn't diminish how good a partition in a 300 win is... just that variation is far more prevalent now.
Large percentage of my friend group has or does guide bear. Most have a 375, some with strong opinions but most fairly agnostic to bullet type. One fellow I know shoots exclusively swift a frames, knowing he's a cheap booger and shoots remington core lok in everything else I finally asked why a frames.... he shrugged and said one did really well on a hunt and he remarked that it was impressive. The hunter was tangentially tied to swift and happy with the hunt and bear so shipped him what amounted to a decades worth of hunting and practice round a frames. When pushed he liked most, but had a frame's so that's what he rocked.
30 cal or bigger driven at reasonable speed with most bullets available, in a platform your comfortable with... gonna be just fine. Because a professional will be standing right there next to you.
