I'm not really sure if Viggo is able to pull of the role of Roland. He's too.. I'd like to say emotional? Or something... I think Roland should be played by someone with more "mysterious charisma".. It's hard to explain exactly what I mean, since Roland is a very emotional character. Also, I don't think Viggo has the right looks for playing Roland.
I've actually started liking the thought of having Javier portraying Roland. At first I didn't like it because I never pictured Roland being of any other descent but caucasian, but somehow I've grown into the thought of him having some latino characteristics. Javier is an excellent actor, and I'm almost sure he could pull of the charisma and "witty" characteristics Roland has.
A couple of days ago, while I was watching The Walking Dead, I realized something. The kid who plays Carl, Chandler Riggs I think he's called, could be an excellent choice for the role of Jake, what do you think? Judging from his looks I'd say he's about the right age too.
As many others, I've always thought it doesn't really matter who they choose to play Jake, because let's face it, there's a bigger possibility for success if it's someone new rather than someone we've already seen everywhere.
Another good choice could be the kid who plays Bran Stark on Game of Thrones. I know, he is still too young, but since it's only recently been announced that HBO will take over the series, it means there's still going to be a couple of years before they start putting it into production. By that time, I think he'll be of the right age.