Web checkin is not going to help in your case. You might as well get there early and use a self-serve check-in kiosk, then line up to get your bags tagged (or just see an agent). Yes, getting there early is probably the best bet.

As for customs forms, probably at your local airport. Otherwise they are available at the U.S. departure area of YVR when you arrive (but that's upstairs).

Or maybe you can get it on the cruise ship.