As others have said, you will not be able to get into the Transborder area. YVR has US preclearance for transborder flights so you must pass through US Immigration prior to entering the Transborder area. You arrive in the US as if on a domestic flight as you have already 'entered' the US by pre-clearing while in Canada. That's why the Transborder area is completely sealed off and inaccessible from other areas of departures.