Hunted and guided in B. C. for several years. I and/or hunters I was guiding took black bear and grizzly in B.C. Got to go on a Brownie hunt and was with a buddy who took one though I did not. For Blacks and Griz I carried a 350RemMag carbine as a backup for the hunter ... sported a Weaver 2.5x. Not real fun to shoot but a great carry gun when packing in. On my own hunts for Griz and my unsuccessful Brownie hunt I carried a Sako in 375H&H sporting a 3x scope. This was a light gun and defintely not one to shoot on a bench (at least not me) but I had complete confidence in it. 45-70 will sure do it. For backup I'd go heavy calibre. In fact, aftrer 40 years of trigger pulling (ok, 50) I will go wiht more gun over less gun. Hearing protection ... heck I like amplifiers!
Meeting these critters face to face in a berry patch you realize that any gun is too little!
Impressive when they stand and roar! And, no need to practice your running!