My advise is to invest in a big can of counter assault bear spray first. Take your time and fire several different handguns and find one that a) doesn't give you the jumps from recoil,b) you can handle and feels good, that way you have confidence in it and your abilities, c) use the handgun as a last resort.
99.9% of people when suddenly confronted by a bear or a mountain lion will have enough adrenaline running through their bodies to fill a bath tub. Pretty hard to rapidly draw a handgun, get a good site picture and get off even 1 good round. The bear spray will give you the time you need to take a breath and calm down a bit.
That being said, i would recommend a pistol with a barrel length of at least 4". the shorter the barrel, the less acurate at longer distances it is. When you add barrel length, you add weight so you need to find the length/weight combo that you can live with. I would also recommend a shoulder rig for doing any hiking or back packing as a waist holster could be a bit cumbersome when you add in a waist strap for the pack, plus the bear spray on your hip.