Good to know that an 08 stang fits the same. That will make looking a lot easier!
The mustang bolt pattern is 5x114.3 and the Grand Prix is 5x115. They’re close enough that it fits fine.
Not sure how much you know about wheels but make sure to pay attention if the wheels you’re getting are hub centric or lug centric.
Most are hub centric, and you’ll probably need rings to equalize the center bore of the aftermarket wheel with the hub on the car.
The factory center bore is 70.3mm I think, so you’ll need something to go between that and whatever wheel you get if the center bore of the wheel isn’t already that.