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Also consider the cruise itinerary. Are you into outdoors stuff like hiking, or do you prefer seeing glaciers from the ship? Some cruises visit Glacier Bay, which is absolutely stunning. Some will visit Hubbard Glacier, or others. As far as ports, the standards are Juneau and Ketchikan. There's a lot to do in both; Juneau is the spot for whale-watching, though. Other ports may include Sitka (Russian history -- fabulous) and Skagway (great scenery and the possibility of a trip into the Yukon).
It sounds from your post that you'd like to do a round-trip from Seattle or Vancouver, rather than a one-way between Vancouver and Seward. Is that right? That should narrow it down some. Please feel free to ask about ports of call.
Oh ... I can change the 2012 to 2013 in the title of your post, if you'd like.