Do I have to register for GST and QST if I take an Ancre address in Quebec?

No, it is not the address that triggers GST and QST registration, but the amount of your taxable sales in Canada and the nature of your activity. Above the small supplier threshold of $30,000 over four calendar quarters, registration becomes mandatory, and non-resident businesses selling to Quebec consumers have specific rules. Your Ancre address then appears as the correspondence address with Revenu Québec, which administers both taxes. Assessment notices and filing reminders arrive at suite 402, flagged as priority, which avoids penalties for unread mail.