I thought the land boarders are also staffed by both CPB and CBSA agents? If I recall correctly, before the new change, you certainly can book an actual Nexus interview at the land border (U. S. or Canadian side), and that interview definitely needs officers from both countries to be present.

Please do report back on your experience at YVR (my appointment is also at YVR in August). I'm curious how it actually works. When I did my Nexus interview a couple years ago, there was no two-part process and I just did a joint interview at YUL after I entered Canada. Now the interview notice is telling me to do the Canadian part at the scheduled time, and then the American part whenever I do pre-clearance on the way back to the U. S. Like I said I suspect the language used in the notice is the same for any interview you schedule as part of the Nexus program. You maybe able to walk into the CBSA office at any time, but you can only interact with CBP during pre-clearance it seems. I imagine it would be CBP that does most of the work for APEC (especially for Americans), if not all. Again it is different from a couple years ago where you can meet officers from both sides in the same office without having to clear security.