I run a Ruger super redhawk alskan in 44mag, I'm in Alaska worried more of brownies than polar bears. I've shot several different loads through mine everything from 240 gr sp to the buffalo bore +p+340gr hard cast that are my personal choice for a defensive gun in the bush. I've only staired down moose so far and not been worried about a bigger gun. A heavy 44 load is near the top of most people's pain threshold and ability to make accurate follow up shot(s). 454 although impressive in numbers is not so impressive in the follow up shot capability for me anyways I've shot handguns my entire life. A lot of the wkend warriors here carry 10mm if you are atv riding or snow machining with the chance of filling you gun with mud and crap then a 10mm glock is hard to beat. You will be in a helicopter most of the time so weight shouldn't be much of a concern, nor mud the diamond d holsters are high quality and will probably out last you. I've always been a fan of 44mag and heavyoads even for deer back home, 44 mag Ruger redhawk in a short or even 4" barrel and some real loads will be more than enough to keep you safe. Getting a bullet to penetrate the central nervous system is the key to stopping a charge dead in it's tracks, usually that means a brain shot. I've seen studies of bears being killed by hunters that had 357, and 9mm bullets just under the hide. Shoot one in the face with a lesser caliber may very well stop his forward progress but if I'm shooting one in a defensive situation I want all the help I can get. Get a Ruger super redhawk thwyre make to take the heavy loads unlike some other brands. Do some checking on hsm and buffalo bores websites on which brand is safe to use their heavy loads in and you'll quickly see which gun you'd rather carry.
About follow-up shots with a big revovler: I watched a video in which a guy shooting a 454 Casull in a FA revolver put 5 shots into 10" at maybe 15 ft in 3 seconds. Not as fast as a 10mm, but respectable. He had to use 2 hands to do it, and was a fairly beefy guy. The revolver in a big caliber is slower with one hand, and in either one or two hands allows some opportunity for slippage, cosnequent failure to cock and fire. I'm a long term big bore revolver shooter, I tried to repeat his work with a .45 Colt, failed. It takes a lot of practice.
A 9mm, a .357, .40 S&W, 10mm, 44 Mag, 45 Colt all offer enough penetration if hardcast bullets are used. Must test to ensure they load reliably and shoot straight. After many years of packing a 4" S&W 44 Mag in the mountains, I've switched to a 10mm Glock 20.
The .44 Mag's .429 diameter bullet gives 10% greater frontal area than the 10mm. It can be made to move faster than the 10mm, though not from all guns. Above 1350 fps or so, greater velocity yields little extra in terms of penetration. The 475 or 500 Linebaugh is far superior to the 44 Mag. in energy transer, but of necessity slower, significantly harder to shoot well, and unlikely to out-penetrate.
With your Glock experience, I think the 10mm Glock 20 is a natural for you. I think the semi-auto is superior to the revolver for emergency work, besides which with a revolver you'll have to familiarize with a whole new manual of arms. Maybe consider using a pistol lanyard; bear attacks have a way of generating stories about people losing guns mid-attack, and the lanyard at least assures your pistol is retrievable.
Many people have used a handgun to turn a bear attack, and the success rate is pretty high. Research the slugs you're using in your shotgun & make sure they're the best for bear. More than one Gov't agency in polar bear country gives their guys 10mms. The Glock is an awesome weapon. Good Luck !
