We had a fantastic time cruising Alaska on Island Princess in Sept 2007. We travelled north from Vancouver, so we were always going to Alaska, rather than leaving it all behind. This means your land tour would need to be at the end of your trip. Pick a route that does Glacier Bay - not all do as a limited number of ships are allowed in each season. In the autumn most of the snow has melted so you can see the surface of the glaciers - in the spring they can be buried and all you'll see is snow. Alaska is great for wildlife watching - whales from Ketchican, bears from Juneau. Book it - you won't regret it!
I'd choose a balcony cabin/mini suite on the right hand side facing the front!
I would suggest Mercury with a FRONT facing cabin on either side . They are huge and the view is to die for. Especially if you are up early,as you will be from UK just call room service and enjoy the hot cholcoate and cookies at 4am and wathc the sunrise. You see the whole of the view there and do not miss anything. it was fabulous.
Outside is a must, even better a Balcony cabin so you can pop out to look at the scenary early morning without having to dress and go up on deck especially as you tend to get into Glacier Bay etc quite early.
Princess is good - Wale watching at Juneau was fantastic especially if you go on a smaller boat which takes about half a dozen people. Also the mountin Rail Trip - White Pass?