Both are GM midsized sedans and they probably share a good deal of parts between them. Wouldn't surprise me at all if the engine, transmission, brakes and most of the electric system were identical.
As far as which car is more reliable that has nothing to do with the car itself. It has everything to do with the previous owner and how well they took care of the car. If they abused the car, neglected the service intervals and just drove the wheels off the car it's not going to be reliable no matter who made the car 10 years ago. If, on the other hand the car was well cared for, maintained properly and driven conservatively over the past 10 years it will be a good car no matter who made it 10 years ago.
A well cared for Chevy is a much better car than a beat up and abused Honda, no matter what the experts say about new car reliability. Used car reliability is based on previous ownership, not the original manufacturer.