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.