It depends on your dealer and how far you are in the process. While most provinces and territories don't provide a "cooling off" period for vehicle purchases (which lets you change your mind about the purchase and get a refund), some dealers might offer it anyway. Afterwards, your only option is to resell the car.
If your dealership has a return policy, ask to have a copy in writing before returning your car. Don't let pushy sales tactics force you into making a premature decision. You have a right to hold off on purchasing until you're comfortable.