Scorsese Does Sinatra

According to this report, Martin Scorsese -- perhaps the most musically minded of working directors (The Last Waltz, No Direction Home) has signed on to do a Frank Sinatra biopic. I vaguely remember him previously being attached to this project some 20 years ago and announcing that Ray Liotta would play Old Blue Eyes.

But who could play Young Blue Eyes? Scorsese loves Leonardo Di Caprio -- and vice-versa -- but I'm not feeling that. I know there will be partisans of Zac Efron and James Marsden (both okay singers, but neither approaching Sinatra range). Who would you cast?