Go With the .300
Rifle59,
If you have a .300, take it and bring premium 180-200 grain bullets. Although the .308 and other calibers have been used to kill bears, they're not what most would consider an optimal cartridge.
If you're going on a guided hunt, your guide's gonna be a lot happier seeing you bring a .300 than a .308. BC is pretty tough country and is quite thick in some areas I believe - you may not get an "optimal" broadside shot at your bear, you may be forced to take a less ideal shot, and you may only GET one shot - that's where the higher power and premium bullet with the .300 will show its mettle. I'd consider using Barnes X, Swift A Frame Safari Grade, or Trophy Bonded Bear Claw.
Good luck, and good hunting!
Michael