It wasn't the Governator Arnie. They just digitally slapped his head from the first movie onto another guy's body. Interestingly enough, as I've read, the body double is the guy who played Arnie in a documentary made about him in his bodybuilding days.
I really wanna see this. Didn't realise it was already out. They should do more promos for it like Transformers 2 did. There is sooooo much Transformers publicity going around atm.