Thomas Jane (whos been hitting the weights for almost 2 years for Punisher 2) for Thor, Kevin McKidd for Loki.
Russell Crowe is another good choice but would cost a fortune.
Theres a difference between The Rock and Triple H.
Rocks character in wrestling showed others how well he would project on screen. He also acted more with that character (look at his angle with Mankind) than Triple H who really just stands around wrinkling his brow and acting mean.
I think Ive only seen one of the Rocks movies. But I doubt Triple H can show the wide range of emotions onscreen necessary to carry a movie. ITs one thing to be large and pissed off all the time. Another to convey fear, sorrow,etc convincingly.
I prefer they got a good actor with good genetics and let him build himself up. IMHO Jane is perfect. He's also a fan, evident from his letter to Quint at AICN when he pulled out of Punisher.