Nexus is irrelevant and your checked bags are irrelevant--when you arrive from Atlanta, you'll go straight to the gate of your flight to YVR without going through any kind of security or passport check. 39 minutes is enough time as long as you don't dawdle between gates. (For what it's worth, in case I'm misreading the "arrows" and you're really starting in Vancouver, you still wouldn't go through security or passport control in SEA. Instead, you'd preclear into the US at YVR and your connection at SEA would be just like a domestic one. So no matter which way you're going, 39 minutes is enough time to connect, again, as long as you don't dawdle.)