On a cruise, I think you are unlikely to see bears. You just won't have the time to get into the wild enough. (Not that it's impossible, just unlikely). The glacier is the best spot in Juneau to try to see them if they are haunting that area. They won't be downtown during the day. There are lots of raptors year round, and whales throughout the summer as well, sea lions, otters, lots of sea life. Salmon jumping late July/early August. Lots of dead salmon after that.

Sitka has a place where you can go see bears if Disney goes back in there in 2017. Hope that helps!