Originally Posted by keithguy
SFO-AS-YVR-AS-ANC differs from PDX-YVR-LHR-MXP and SEA-YVR-CX-JFK. PDX-YVR-LHR is a US to International connection, which requires a cursory check by Canadian immigration. YVR-CX-JFK does not preclear US customs, so the procedure is the same as PDX-YVR-LHR. YVR-AS-ANC does preclear US customs, so that's where the problem lies.
Basically, if YVR AS agents let connecting passengers into the pre-cleared, post-security YVR US departures area from the arriving aircraft, then it should be fine. However, if any immigration clearing is required, there is a slim to none chance of making it in 46 minutes.
Keithguy is pretty close. In the busy summer months with cruise ship traffic, AS develops a YVR mini-hub and coordinates connecting pax travelling north to ANC/FAI and south from the same. Only adjacent transborder (US->US)gates E83 and E84 are used for this purpose and have a holding area where pax can sit until boarding their next flight and DO NOT have to undergo any Canada or US immigration/customs formalities. This is a fairly unique set-up and has been used for the past couple of years.