When push comes to shove, I would be far more worried about an aggressive black bear than a grizzly. Grizzlies are notoriously near sighted and a lot of them get shot charging. I am in no way telling you to take the chance the charge isn't a bluff by the way but by far, the vast majority of those charges are just that. I don't know why they get aroused to charge. Maybe curiosity, maybe we look like a bear standing? Who really knows.
I've been charged by Grizzlies and only in one case did I have to shoot it. I doubt bear spray would have stopped this animal. I have a tried and true method. If I notice what seems to be an aggressive bear moving in my direction, I pick a spot that I think it will cross through on its way to me and place the cross hairs of the scope on it. If I see hair in the scope, I am already in position for a quick, accurate enough shot to at the very least stop it, knock it down or turn it around.
By the way, I seem to attract bears. Brown bears, Black bears, Grizzly bears even Blonde Phase black bears. I see bears of one sort or another every time I'm out fishing or hunting. About ten years ago, I was coming back from building a blind on the edge of the High Tension Hydro line right of way. I didn't bring a firearm with me as I had about 20 pounds of hand tools and other stuff with me. This darned 5 foot black bear started to follow me. I had an axe and a sledge hammer but I'll tell you right now, you only have one split second chance to get it right.
I ended up picking up a 4 foot long, dead Mtn Maple butt about 3 inches in diameter. This gave me something I could easily control and use as a ram or swing like a club. I ended up whacking the black across its nose. I was scared as hell, once it got that close. I hit it with everything I had. There was a nasty, loud crunch and a squirt of blood. That poor bear bawled like he had been scared out of his wits. He gave a snort of blood, turned around and ran. That's about as excited and scared as I've had the privilege to be.
Funny thing, all the while the bear was following me, it never once growled, raised its back hair or made any aggressive moves. It just kept getting closer and closer. It stopped once to sniff the air but that was it. Maybe it was just curious??? Those scientists in Alaska that were studying and living with black bears and felt they were part of the family, until they were invited as the main course for lunch. When wild bears get to familiar or close, time to do something about it.
I shoot at least two per year. We really like the meat and there is nothing better than a corn silage fed bear around the middle of April. They've had time to clean out their systems and bulk up a bit on the silage. Marinated from the inside out. Farmers and Ranchers hate them for that. They make a hell of a mess of the silage pits and when they get to that black liquor on the bottom, they turn into mean drunks.
I only have one argument against pepper spray. If you get the wrong stuff, it's ineffective. Also, you can't predict the direction of the wind. The sprays that squirt a stream, rather than a mist are what you need. They will penetrate the wind for 3-5 yards, depending on velocity.
One thing that bothers me with some folks that insist on carrying a firearm for bear protection. They carry them in well used areas. I can understand why but many people in well used camping areas freak out at the sight of a shotgun or rifle. Causes all sorts of problems that may be even worse than bears. If you're going to carry a firearm for bear defense, be discrete if you are in a well used area. That's where bear spray really shines. One other thing that will startle even the most aggressive bear is one of those marine sirens that mounts on a can of compressed air. I know a rancher that has an electric siren that is painfully loud and he uses it to keep bears, ducks and geese out of his silage pits, which are right beside the Shuswap River. I was skeptical at first but, I must admit it works and works well. They don't seem to get used to it either.