Thank you for all the advice so far. For whatever reason I had always thought slugs were poorly regarded for bears, but it is nice to see both are viable options.
To respond to a few questions and/or comments:
I don't figure I'll actually have either on my while I'm actually fishing, that would be what the .45 Redhawk would be for. I think we'd just like to have a worthy long-gun or two around camp when we're filleting fish, cooking or what have you. A number of us are hikers and know the protocol for food/bears/and campsites.
Additionally, I'm not particularly skilled with either weapon, but will practice before the trip. For what it's worth, the 12ga has a 28" barrel though I'd consider getting a shorter one and maybe some ghost ring sights for it. The Guide Gun already has XS ghost ring sights on it.
I've got a little experience with black bears from camping, and I know that most situations can be avoided, and there isn't a 100% effective defense for all situations. I think our party's mindset is simply that if the worst were to come to pass in the wilderness with no help around(something like Kodiakbeer's or rajb123's situations which I'm sorry to read about), we'd like to have the tools available to bring it to an end.
Because I'm expecting to have some lengthy free periods coming up, I'd also like to take a first aid class or two, especially something geared towards backcountry situations where help may be days away.