Not sure if you are buying the warranty with a new car or with a used one, but it does make a difference in the cost. Any GM dealer can sell a GMPP for any GM vehicle so shop around. I received a quote for Fitchner (sp?) Chevrolet in Montana, after I had already purchased GMPP for other two vehicles from them, and it was considerably less than the dealer quoted us on the one for the SRX. Amazingly, our selling dealer found some "Cadillac money" that allowed them to get below the Montana pricing.
Usually they only need the VIN, miles on the vehicle and what term, miles and deductable you want.