We ran into the same problem Sea Tac - Vancouver. HAL was sold out, (although friends who took it said it had lots of empty seats), and we had to take Quick Shuttle service which left a couple of hours before the HAL trip.
That lady driver didn't know where her pickup stops were and we toured most of Seattle while she kept assuring us and a couple on Royal Caribbean that we would get to our ships in plenty of time because she, "had a schedule". Yeah, maybe she did, but it sure wasn't the same one the company published. We arrived at the far diagonal end of Canada Place and after clearing Canadian Emigration and U.S. emigration and hiking half a mile to the HAL embarkation desks, they rushed us on board to finish processing the paperwork. (Maybe having a suite helped). They literally were hauling the gangway as we cleared ship Security.
The return trip was on a HAL but which was much better but it also parked at the far distant end of Sea-Tac airport and it was a long hike with luggage to get to airline check in.
Maybe flying to Vancouver is a better way to go.
