Procedure seems to have changed substantially. WS=>WS coonection last week was:
Go to domestic connection clearance after you use the kiosks (need to show onward boarding passes) on the right side of arrivals hall as soon as you get off the down escalator, line up to pass CBSA, boarding pass check/scan again, board shuttle bus that takes you to domestic airside (one of the gates at the base of the old domestic (C(?) pier). No security recheck.
Think this works only if you have no checked bags or flight is approved for no checked bag customs clearance.