First things first. Never go into the woods overnight without a wildlife resistant canister for all your food and any other items that might attract wildlife. Never, ever. Even if you aren't in bear territory; bears aren't the only wildlife that can and will get into your stash and/or potentially attack you and yours. The outdoors community needs to take personal responsibility for disturbing the habitat of wildlife, and normalize the practice of always carrying a bear canister.
That being said, while I understand this thread is probably meant to be only semi-serious, I don't regard this as a joking matter.
I would not recommend any knife for bear defense. I would not recommend any firearm smaller than a .44 Magnum, and that *only* if you are loaded with ammunition specially designed to deal with dangerous game, in a double-action revolver, and that should be your absolute last resort.
This is not a subject to joke about. If a bear surprises you (or vice versa), and that bear attacks, you may not have time for a second round. A single-action revolver is the most reliable, mechanically speaking, but in the event of a surprise attack, it's too slow. The double-action revolver is only slightly less mechanically reliable, but will give you at least the chance of a follow-up shot, if you can manage the recoil--which is why you absolutely need to go to a range and practice with that revolver and the heavy duty ammo, so you are at least familiar with what it is going to do.
And I would recommend a stainless steel revolver to help cut down on the recoil, unless you are strong enough and experienced enough to cope with an alloy frame in a calibre that powerful. The alloy frame S&W revolvers really cut down on the amount of weight you will be carrying around, but the recoil is immense. Think Ruger Super Redhawk Alaskan...that's why it's called the "Alaskan" model, it's specifically made for grizzly protection, and .44 Mag is the smallest calibre they make in that model, because it is widely considered by experts to be the smallest calibre that stands a chance against a grizzly bear.
Again, this is your absolute last resort. You should never be in the backcountry in bear territory without firearms. And your first choice should always be a rifle. If you are carrying solely for wildlife protection, a matching .44 Magnum lever action carbine is a good choice to pair with the revolver, since you can use the same ammo, and it will hit even harder coming out of the rifle. .45 (Long) Colt is a good choice for this, as well, since there are bear protection loads available for that calibre as well as lever guns and double-action revolvers. Otherwise, if you are there for other hunting purposes, if you are in grizz territory, you should have *at least* a .30-06 Springfield.
Don't even think about trying to take on an attacking bear with a knife. If you ever find yourself in that situation, it's because you f'd up and didn't prepare properly.
If you are ever attacked by a bear or any other creature, anything and everything you can bring to bear is a weapon (pun intended). Do yourself a favor and make sure you bring the right tools for the job, so you at least have a fighting chance.