GT-03 has been announced as Megatron, which isn't a big surprise, after having Optimus as GT-01.

Just like the previously announce Super GTs, Megatron is a fully painted race car in white, black and red, using the same mould as the first two... and comes with his own Race Queen (scantily dressed girl figurine).

The link shows Megatron as just an artistic illustration, but also has more images of the Optimus toy.