Hello @Zee164
No normally any existing reservations will remain with the same cancellation terms that were in place at the time of booking and will not be cancelled by Airbnb. Are there any local restrictions on short term letting for Quebec City that may be in play here?
If you change to the new 32 night minimum stay for future bookings you will automatically fall in Airbnb's long term policy which is detailed below:
https://www.airbnb.com/help/article/245
All the best
Joëlle