Alaska is a target rich State to shoot some really breathtaking shots. But, you do have to be careful. YOU will not be at the top of the food chain. That place is firmly secured by the Polar Bear. You don't want to get close to these guys. If you go looking for bears, take as long a lens you can get. The absolute minimum would be a 100-400mm zoom. Alaska, is also home of some really big grizzly bears, these guys are no slouch either. For the beautiful panaramas you may want to invest in a ultra wide angle lens, like the EF-S-10-22mm. It does not have IS, but you can get some stunning wide angle shots from from the trusty tripod. Also, the 10-22 gets rave reviews of image quality from some of the major reviewers, Ken Rockwell, give it a "L" quality review. I wouldn't spend any extra money on a EF 70-200 f2.8L IS USM. It is a large heavy lens. But I would opt for the EF 70-200 f4L IS USM, it is much lighter, and has good IS, and will be easy to sling around on those eagles. You fail to mention what lenses you now have, but a good mid range telephoto would be good to have for the trip. Shots taken from the cruise ship should be hand held, because of the vibration of the ship will pass through to the tripod. So, any lens you shoot with from the ship should have IS, if not you may have to up your ISO to 1000 or more, and shoot at a high shutter speed, to keep out blur of movement. For that mid range telephoto you may want to look at either the EF 24-105 f4L IS USM, or the EF 24-70 f4L IS USM, both are Canon L quality lenses, and reasonably priced. Those lenses I have suggested will fill all your needs for your trip, with the sharpest quality lenses for your camera. I would suggest you purchase a refurbished 7D to upgrade your camera body. The 7D is the best wildlife camera available now. You can get one from Adorama, now on a refurbished special from Canon. You can also buy the lenses refurbished from Adorama, and B&H, and even used from KEH and save a good amount of money.
Enjoy your trip.
