I was there morning, afternoon & evening. Good light at all times. When you are at Brooks, the weather will likely be overcast if you are lucky; rain if you are unlucky.
Most important is to learn when salmon are running; otherwise no bears.
I found I used 80-200, 300 & 500 about equally. That was three years ago when I shot film. With a 1.5 crop on a DSLR, a 300 is probably sufficient for the longest lens.
http://www.pbase.com/image/26488498