BEAR SPRAY.
Or, a clean human mind loaded with a sharper awareness of your surroundings over a good charge of "Stay far away from the big stuff with teeth."
There have been cases where 3x .300 WM didn't stop a bear in attack-mode. A gent with a .454 Casull needed to empty the mag after quick drawing and pretty much spray-praying, and the only reason the bear dropped is one of the shots managed to slip into the brain-box. One of the largest grizzlies dropped to a .22LR because it's what the victim had on them as the bear came down on top (through the mouth and again into the cranial cavity)
The "what caliber/gun/bullet" case has been beaten ad-nauseaum across the forums repeatedly, and the only sage advice I've seen, and heard repeatedly work, is Bear Spray - there's a reason guides and wildlife control officers recommend it before firearms. Not to mention discharging a firearm and worse wounding/killing a bear in a national park makes getting attacked seem like a worthwhile alternative...