We've sailed to Alaska on HAL, Celebrity, and NCL. We were happy with all 3. I'm sure we'd be happy with Princess too. We loved Hubbard Glacier. We loved Glacier bay more. Celebrity doesn't go to Glacier bay. HAL and Princess do although not every ship.
As Donna said, sailing round trip from Vancouver is much more "inside" than the trip from Seattle. Also you hit open sea on the route to Hubbard Glacier. So if you have sea sickness concerns you'd be better sailing from Vancouver and including Glacier bay. Of course, you're on the ocean and never can predict the weather.