More important than caliber is using the correct bullet. Use solid hardcast style bullets. No hollowpoints which will flatten, not penetrate deeply enough. As far caliber goes 44mag or better for pistols is good. But rifles are far better. There are any number of bear loads available for 45-70, 444 Marlin etc.
An M2 mounted on the bad of a pickup truck is probably best, though, for Grizz.
It's best to be fully prepared.