Matt Bomer as Superman is a good choice. There are some who think he would be good as a live-action Superman, and I think he could pull it off, though he's a little short for it.
Honestly I think computer tech used in making films is getting to the point where that won't be a problem anymore.
I think a Superman movie is going to demand enough elaborate VFX without going to the unnecessary trouble of altering the main character's height. I mean, it's necessary for something like Captain America
where the hero undergoes a major change in physique in the course of the story (though I still think they should've hired real Little People to star in the Tolkien movies), but for a Superman movie it makes more sense just to cast someone who's got the right build for the role.
Or else just not worry about it. Hugh Jackman's a whole foot taller than Wolverine is supposed to be.