Hey! You’re definitely not the only one who’s run into this — it’s actually a pretty common issue. Unfortunately, the AAMC system doesn’t let you reschedule across countries through the regular online portal. Even if a seat opens up in Seattle, it won’t let you switch from Canada to the U.S. without canceling and re-registering entirely.
Calling AAMC is really your best shot, but yeah... it’s tricky because those last-minute spots tend to open late at night, outside of their phone hours. I’ve had students in the same boat, and sometimes if you call during business hours and explain the situation, they’ll flag your account or walk you through what to do if a spot opens.
That said, if it looks like a hassle and your Canada plans are solid, it might be worth sticking with your original test site just to save yourself the stress... seems this was many years ago but in case anyone else comes across this issue...