#1, #2, etc.
#1). Many, many articles over the years in the likes of Outdoor Life and Sports Afield recommended carrying a whistle around your neck and blowing it hard before going around curves in bear country... If not too obnoxious, you might consider wearing a bell or three (small). Few bears are looking for a confrontation... They eat a lot of carrion, already dead...
#2). With the reduced number of bears, the bear spray is responsible. Hit them in the face and let them get away if they will. Beware the wind. You "get a whiff" and you may wish the bear would eat you...
#3). Couple decades past a rabbit hunter in Outdoor Life I think, told of carrying a Ruger single action in .357 while rabbit hunting with a shotgun. (5 shots back then, hammer on an empty chamber.) His buddy carried a surplus Luger back when they were common. Of course they had a "run in" with a bear. Each emptied his handgun. All the Luger slugs were found in the fat under the skin. The .357's that hit, one complete miss, penetrated the body and killed the bear. Where to shoot. You put a big heavy slug into a shoulder and you should be able to out run the wounded bear. Hitting the brain, unless you have nerves of steel and some drugs (downers) to boot, ... Not a risk I would care to take...
#4). Mr. Keith did not feel undergunned with the WW I .45 ACP revolvers on the Rocky Mountain bears, black or grizzzzz... A big, heavy bullet at any velocity is going to ruin their day, don't imagine they like the noise and if in the vitals end their life, probably. Now if you were "bear hunting" and might want to "take a bear" at 50 yards, then, yes, .44 Magnum or larger.
For self defense, the NUMBER ONE RULE, the best gun is the one you will, WILL have with you. Better a .38 noise maker than a stick. (or knife.) The cowboy copies in .45 Colt (aka Long Colt) are handy and adequate. There are .44 Special snubs. And there are double derringers, over under in .45 Long Colt. (or...) How much you want to spend? How much you want to carry? How much you want to practice? Gun Digest Annual has a list and many pictures of the "guns in production" for that year. You might care to review the handgun options. Discretion is the best part of valor and the bears are getting "thinned." Then there are the hassles with the authorities. Best of luck to you in the great outdoors.