Buy and shoot the largest gun you are comfortable shooting and one you can shoot good. (no need for an ultra super magnum if you can't hit the broad side of a barn with it) Obviously the bigger the better when it comes to Brown bears but that being said the 7mm mag is more than capable of putting down a Brown bear...even a big one if the the correct bullet is used and your aim is true. Good luck and I hope you indeed do decide to go.
Oh and one more thing...they are A LOT bigger in real life up close than you think. I can almost guarantee you the first thought you will have when you do see one up close is "Did I bring a big enough gun"!?!