Have a great cruise...you will love Alaska! We found that Juneau was the best port and unfortunately did not have a whole lot of time there. We took an early morning whale watch and it was great! My advice...go with a SMALL boat tour, I believe we had 20 people on ours. The captain of the little boat told us that the humpbacks have learned to stay away from big ships because they are getting killed due to so many ships going through Alaska now. We didn't see a single whale from our Princess ship, and Alaska is loaded with them during the summer months as they migrate from Hawaii. Remember...GO LITTLE BOAT!
We also took a hydroplane ride to an island off of Juneau where the brown bears are. It is a spectular thing to do on a cool day, unfortunately it was 90 degrees that day and the bears would not come out. They usually land the plane next to a beach area where all of the bears congregate. We saw one from above and that is all. I wish that we had gone to the glacier....heard it is incredible! Good luck!