I can see Russell Crowe as Tom Hagen perhaps. Also, for what it's worth, I wouldn't eliminate Leonardi DiCaprio either (I know most disagree). I think he could play a young Sonny.
TIS
"Mankind must put an end to war before war puts an end to mankind. War will exist until that distant day when the conscientious objector enjoys the same reputation and prestige that the warrior does today." JFK
