Saleen was hired to make the shell of a new Camaro for them to use in the movie. Since the Camaro is only a concept, they needed to have some made for the movie. Saleen used the shell of a GTO to make the Camaro.
It will be BumbleBee in the movie.
I have a Transformer diehard that works with me here. Anything you want to know, he will know.