All seats in that year range will bolt in place but the wiring harness in the car will vary depending trim level and options. The SSEi and GXP do have a power passenger seat. Some cars have side air bags, some don't. This also holds true for heating elements. To swap the entire seat it's more important to match options (for example, you don't want to put a power passenger seat into an SE or SLE or you won't be able to move it). If you install a seat with an airbag into a car without, the air bag simply won't work. The other way around and you'll have an air bag warning lamp. Seat heaters will also only work in a car that had them originally, but if the car doesn't, it really won't matter. 2003 saw a change in the style of upholstery (and therefore the foam as well) but the seat frame/track bolts right in. Since the OP has an SSEi, my guess is the only question applicable is whether or not they are heated. Likely in California it would not matter if he did install one that wasn't heated since they are probably never used anyway. Finally, it is important not to use leather from a seat with manual lumbar adjustment on a seat with full power since the holes for the controls are different.

also any 00+ Deville, 99+ Seville, 00+ Lesaber and 00+ Aurora seats will physically bolt up, but may not match your wiring