YYJ is a particularly rough destination, because there's no US preclearance there. That means YYJ flights are taking up baggage claim and immigration capacity at the already-bursting-at-the-seams international arrivals facility in Seattle.
It wouldn't surprise me at all to see YYJ return once the new IAF is finished someday, particularly if Delta is able to migrate a fleet of smaller aircraft that are more appropriate for the route out here like the CR7.