Have done this two times - the first when driving back from Denver to BC in November, the second the end of December, after dropping relatives at Seatac. Couple comments:
CBSA accept a PCR test or IDNow (and a couple others but they are not easy to get). PCR takes 24-48 hr for results, IDNow takes within 24 hours. We did IDNow both times, first took 25 minutes, second took about eight hours. Keep in mind, you also have to use ArriveCan (online app) to cross into Canada.
Walgreens, and a few other pharmacies, are contracted by the government to do tests to anyone who books an appointment, for free, regardless of country of citizenship. However, it is difficult to book an online appointment without a US address. We used our son's address in Denver and when showing ID at the Walgreens drive-through, we showed our BCDL and they had no issues with that, both times.
First time we had to book at Walgreens in Twin Falls Idaho, as could not find any available appointments anywhere else (tried in Salt Lake City and Washington State, to no avail).
Second time, I had to stay up until midnite on a Thursday to book in the morning on the Friday of the next week, because Walgreens have their appointment schedule booked instantly for the next week (it opens up a day's appointments for a week hence just after midnite and they go fast).
If you are driving back, I would suggest you book online at Walgreens in the Portland area, as they seemed to have the most available bookings. Anywhere in Washington State, because of the border and Seatac, is usually very difficult to get a spot. If flying, get one before boarding as you need to prove your Covid status to the airlines if an International flight.
If you are willing to pay, there are a few places near most airports which fly international. No Covid test is required to fly domestically, so domestic airports will likely not have test facilities. Keep in mind, the associated cost is $180 - $360 USD per test.
It is a pain, but doable.
Marv
