Many people believe doing the land first is better. You have three or four busy days on land and then you can relax for seven days on the ship. However; that can be busy too, depending on the number of port stops and which activities you do. One big difference is once your on the ship you won't have to unpack for seven days. With the land your packing/unpacking. Ending your cruise in Vancouver may cut off a little flying time home.
There is a traveling show called "Alaska Onstage". It is a team of Alaska experts that travel around the US talking about Alaska. Even the experts say it really doesn't matter which direction you start with, because an Alaska Cruise/tour is a busy schedule either way.
I would pick the ship, date, itinerary, that works best for your vacation schedule and not worry so much about the direction.