When people talk about the 44 Magnum being underpowered for Alaska, they are usually talking about shooting the 240 grain JHP ammo at Walmart. This isn't the ammo that you want to carry for bear defense. Your Redhawk will shoot this ammo from Buffalobore- https://www.buffalobore.com/index.ph...ct_detail&p=54
and this ammo from Garrett- http://www.garrettcartridges.com/44hammerheadplusp.html
I also have a Redhawk 5.5 inch 44 mag. I can handload a 355 grain Beartooth bullet to 1225 fps and a 325 grain Beartooth bullet 1325 fps (much cheaper than buying Garrett or BB ammo, by the way). Those loads are at a completely different power level than the 44 Mag ammo at Walmart and start to approach the bottom end of what a 454 can do.
But the main consideration is - can you accurately shoot those loads? There's no point buying a 454 Casull that you can't handle.
If I was in your situation, I would take the Redhawk with some BB or Garrett loads, and a 12 gauge shotgun with Brenneke slugs. When you get back from AK, learn to reload for the 44 Mag and work up your own bear loads.
A couple more advantages to the RH 44M over a single action 454 -
Practice ammo is cheaper and easier to find. 44M brass is cheaper than 454 brass. I sometimes find 44M brass in the buckets at the range. I've never found 454 brass at the range. 44M bullets are cheaper and easier to find for reloading. It takes a lot of practice for most of us to become accurate (meaning to stop flinching) with the big bore guns.
There are people who shoot nothing but single actions and are very proficient with them. The rest of us are better off with double action revolvers. When that bear knocks you down and is chewing on your head and you are trying to hold him off with one of your hands in it's mouth and shoot it with the gun in the other hand, are you going to be able to cock the hammer after every shot or do you want to just pull the trigger 6 times?
But the main thing is that a 12 gauge with Brennekes is far better than any handgun. They are just hard to carry when fly fishing a river.