I am of the school that says for perhaps your only cruise to Alaska you should sail on an itinerary that includes Glacier Bay. The major lines that visit there are Princess, HAL and NCL. Why Glacier Bay, you ask? The other glaciers that appear on itineraries are often missed due to ice, but I cannot remember hearing a ship missing Glacier Bay. Hubbard Glacier is equally impressive, but it can be missed, primarily due to fog. Alaska should be for the itinerary, cruise line perks secondary unless you are traveling with children.
You also need to decide if you want to sail round trip from Seattle or one way from Vancouver. I would go to cruisetimetables.com and put in Glacier Bay in ‘cruises to…’. It will tell you who calls there and their itineraries. There is also lots of good advice and experience on the Alaska board here under Ports of Call. EM