I would recommend one that leaves out of Vancouver.. Those lines mentioned above plus Celebrity and others do that of course and I would be OK with them. There are others..... but i do not have any personal experience with them. RCL has a round tripper out of Seattle too.
Vancouver departure gets you way more scenery in and along the Inside Passage. Have a buddy from Seattle that just did another trip out of Vancouver and swears he won't leave from Seattle again. Well not until he does anyways. Budget and ships for kids will always be at play but the scenery can't be beat on a trip out of Vancouver. Out of Seattle you sail outside Vancouver Island in the Ocean..no one between you and Japan. Inside lots of trees and Mountains and yes even whales and Eagles... oh My.