Though I have'nt cruised with Carnival in some time (I now cruise with Celebrity) I have cruised to Alaska.
The cruise started in Los Angelos stopped in San Fransico, Seattle, Vancover then itto Alaska stopping at all the major ports.
I can tell you Alaska was one on the most beautiful places I have ever been to. I have been to just about every Island in the Carribean, and the Panama Canal. (Bermuda is right there at the top of the list also)
The tours are fantastic but very pricey. My wife and I took a helicopter tour and landed on top of a glacier, FANTASTIC but the cost for both about 7 years ago was close to $450.00
Most of the tours are very expensive but they all are wonderful...Everything from a kodiac raft tour to taking a old time train into a gold rush town.
The price of the Celebrity cruise with tours and our airfare from the east coast ran about $7000 after all was said and done, keep in mind that was about 7 years ago...But if you can pull it off trust me you will not be dissapointed. (with Alaska that is, Not sure about the Carnival line because we cruised with Celebrity. But I am sure it would be fine.