Just to post my experience:
Upon landing in YVR there was the option to go directly to US Customs for the Alaska Air flight to Seattle (I assume same for DL flights). They did not operate Global Entry kiosks on this path so you'll still need to fill out one of those declaration forms. X-ray line was long but I asked for help due to my next flight departing in 25 minutes (Incoming CX flight was delayed 2 hours) and they bumped me to front of line. Made the flight and saved myself from having to kill 2 1/2 hours in that little commuter terminal for the flight to SEA.