Excellent- thank you sooo much for this first-hand confirmation! It seemed to be the logical checkpoint, considering the test needs to be timed for the US to CANADA portion of the flight.

I am flying ATL-SEA-YVR and I was really hoping check-in at ATL didn't try to make me show my test, since my results may not be back until the afternoon.

Incidentally, what's the price of a rapid PCR test at SEATAC? Might be cheaper to do another free test at a SEA Walgreens and reschedule my flight if the one I take in ATL isn't back in time! LOL!