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Most cruise lines will allow you to deviate your flts (Pick your own) with a fee involved. Ask your TA when you get to the booking point. Some with their Frequent cruiser clubs have that built it at a certain stage. I have only done the Inside Passage which is up and back from Vancouver but I have read that if doing a land tour most suggest to do it first. Vancouver is a great city to spend time in and yes the same can be said about Seattle. Consider the borders crossings and time involved in your plans if you are leaving from Vancouver and flying into Seattle.