OP: if you're referring to the domestic side C gates (for AC flights), there are two entrances, NEXUS/Priority and the regular entrance.

The entrance on the left is for both NEXUS and priority, though NEXUS is more prominently labelled. Once past the greeter, there are two lane choices, NEXUS on the left and priority on the right. As others have noted, they often merge again to an agent who will direct you to a lane.

However, from time to time, NEXUS goes straight to its own, painfully slow, scanner. This coupled with the fact that every Tom, Dick and Harry in Vancouver has a NEXUS card, usually means the priority line is a more reliable choice. Choose this line regardless.

(To others here, I say an out of comission exclusive NEXUS lane is to your advantage.)

In my experience the procedure, though different at YVR, is no more time consuming than priority security at YUL or YYZ.