Skip the float trip. I've done it and it is one of the few poor tours out of all I have taken, in my opinion. Very brief distant view of Mendenhall, rest of trip is trees and backyards. For the cost whale watching is a far better deal.
As for your Mendenhal/wildlife quest?? This is a whale watch- with humpbacks seen on 100% of the trips and a stop at Mendenhall glacier visitor center. You can also book with Orca Enterprises- bonus is smaller boat and see if they can drop you off at Mendenhall? Then you can leave via shuttle bus when you wish. This is especially worthwhile for someone wanting some hiking.