National Forests allow firearms, National Parks generally don't.

I personally don't see tasers as being particularly useful against wildlife. As ponder pointed out they're short range devices. I don't want to wait until a bear is 15 to 21 feet away. Not to mention they're also around $300 dollars. (Taser C2, 15 foot range, $300-$350 price tag, extra cartrige $25 http://www.taser.com/products/consumers/Pages/default.aspx) Pepper spray is highly effective against bears and doesn't cost nearly as much ($40-50). Pepper spray has about double the range of a taser. (http://www.udap.com/Bearspecifications.htm)

Given the choice between a gun, taser, and bear spray against a bear, I'd chose bear spray.