General Motors has shared bodies across model lines for many years. Buick and Pontiac is a good example. As far as fitting goes, any seats from another model that shares the body will fit. The main difference is the style and fabric of the seat upholstery. The seat frames are the same and the front seat cushion frames and backrest frames are interchangeable.
If you are planning to reupholster the seats, you should gather together all the seat frames, test fit them, and then do the upholstery.