Ted deCerchio
It's probably easier or more viable to e.g. have Harry Connick a singer to play the part of Sinatra. Conversely,I believe it would be more difficult to make actor Mark Ruffalo sing "I'll Never Smile Again." This is my belief,not necessarily factual.If Scorsese is going to dub the music,then the actor might have an advantage over the singer because the actor does not have to sing. Otherwise,I believe the singer can make the better adjustment to act than vice-versa.
Ted DeCerchio Upper Darby,Pa.

Ted deCerchio
The several-part television biography of Frank produced by daughter Tina in the 1990's was very good,not just because young actor who played Sinatra was from same High school (20 years later) I attended, but because actor did an excellent job playing the 1st half of Frank's singing career. Correct me if I'm wrong,but songs were Sinatra's, dubbed into musical part of the series.I don't know about the other actors,but I still think Harry Connick could vocally pass for Sinatra as Kevin Spacey did for Bobby Darin in Beyond the Sea.