I really don't know if there is anyone that is capable of filling Supe's boots like Christopher Reeve. He was the quintessal Superman... he was handsome, pleasant, helpful, brave, thoughtful; 'the world oldest Boy Scout', like Lois Lane said. And Reeve was not too muscled, just cut. If he got all buffed out, it would have looked very foolish.
Just like Micheal Keaton as Batman, they should have left it as it was, a great series... both actors were perfect as their characters- deviation will tarnish the original image, both of the actor and the role, a otherwise perfect mesh.
Hopefully Hollywood will have some sense of patriotics and cancel the next movie... not everything needs an updated SFX remake. Just like the Ten Commandments, or a Streetcar Named Desire, just leave it as it is.