If you can get a permit I'd suggest a .44 mag in a revolver (S&W or redhawk) 6 inch or shorter. Semi auto can jam and they are heavy. get a double action revolver not a single action like a 454 casull. They are extremely slow to reload.
A hand gun on your hip is always easy to get access too. A shotgun or rifle is like not being able to reach the toilet paper out in the bush. When you need it bad, it's just out of reach. The big magnums like 454, 500 etc have such a recoil and twist, if you had to shoot with one hand, the gun can twist right out of your hand. Not good if you need a second shot fast. Good luck
Gene, I'm a revolver guy, but I gotta disagree with you. Most auto pistols weigh under 40 oz, but the revolvers you suggest are closer to 50. As for concerns over semi-autos jamming, that got worked out nearly 100 years ago, and flies in the face of the fact that every cop in the country and many soldiers have one on their hip. When a revolver jams you can have a real problem; because if the jam is caused by a bullet jumping it's crimp in the 11:00 chamber, there is no convenient way to clear it. The gun won't fire and you can't swing out the cylinder to remove the cartridge. If the auto pistol jams, it is usually the result of one of three stoppages: a failure to feed, a stove pipe, or a double feed, all of which are easy to clear if you understand how. In the bear defense scenario fast reloads are seldom an issue; fast shooting can be though, you've either solved the problem with a couple of rounds or you're dead or badly injured. In the case of an attack by a sow with a pair of second year cubs; all that will save you is the grace of God, and some very fast, accurate shooting, possibly backed with fast reloads, where the light recoil, large capacity, and fast reload capability of the semi-auto provides a distinct advantage over any revolver. Fast reloads suggest something other than the individual loading of cartridges, so consider the difference in bulk between a magazine and a speed loader.
The SA revolver is slower to reload than a DA, except that there are tricks to help things along. When you've fired your second round with a SA, the first spent cartridge is now in line with the loading gate, so that round can be quickly exchanged for a fresh cartridge, then you can rotate the cylinder to recharge the second chamber, or if the situation demands, you can continue to fire. Maybe thats why the good guy never ran out of ammo in the old westerns!
I think the durability of the SA trumps any advantage the DA might have, but that's just me and others are free to choose the gun they prefer. Some folks just don't like the SA's handle, and find the stocks of a DA more comfortable. I seem be be the opposite in that the hump of a DA grip frame really pounds my hand under recoil, and the rubber inserts on the SRHs seems to increase the sensation. I agree with your comments concerning the controllability of full power loads in the big bores though.