I highly doubt a 2000 Seville could beat a Camaro or Trans Am of the same year. From the factory the Seville has 300 hp and 295 ft-lbs of torque. The Camaro and Trans Am have 305 hp and 330 ft-lbs of torque.
Now they are pretty close in power but here is the difference. The Seville is HEAVY, real heavy and big. The Camaro and Trans Am are a lot lighter. Plus when racing from a dig (stand still) the 35 ft-lb difference in torque will really make a difference. You're looking at over a second difference in 0-60 times to start with 5.3 for Camaro and Trans Am and 6.9 for the Seville. Mustangs tend to be slower than Camaros and Trans Ams but still a bit faster than the Seville.
Now if the Seville is racing the V6 versions it would be closer, in this case the Seville would probably edge out the competition. The closest race would be the Seville against the V6 Mustang
But if he were to race any of these cars and they were stick and the driver did not know how to drive stick well, the Caddy could very well win then.
9 out of 10 times the Cadillac will lose.