Under the GST system, trade-ins of road vehicles are subject to the same rules that govern sales, purchases or trade-ins of other used property.
This is also the case, generally speaking, under the QST system. The QST applies to the estimated value of the vehicle. (The tax is collected by the Société de l'assurance automobile du Québec.)
For more information on this subject, particularly with respect to sales of used road vehicles and trade-ins accepted in sales to third parties or in the leasing of a road vehicle, consult brochure IN-624-V, The QST, the GST and Road Vehicles.