If a black bear attacks you, it's because you've either startled it or you look like a potentially tasty meal. Making yourself big and noisy and trying to scare it off or fight it off is the only way to go.

If a brown bear attacks you, she's not planning on eating you, but you may have invaded her space. In which case, playing dead may be the safest route.

In either case, bear mace/pepper spray may work against humans, but it's pretty unreliable against actual bears...