I have a slightly different query.
I'm planning to fly LHR-YVR-SFO. I'd like to spend a few hours in Vancouver prior to connecting to the SFO flight.
Presumably, to avoid any checked bags being lost, I need to go to the bag identification room first so they are checked through (assuming this still exists - been a few years since I last did this at YVR).
Is is then possible to back-track through the airport to Canadian Immigration, or will I be forced to carry on to the US pre-clearance desks? I'm interested more in practice than theory here - as in, will I be just be herded onward if the place is busy, or is it *always* possible to re-trace my steps through the terminal?