I noticed in some of the deleted scenes, like after Fanucci gets cut and Vito and Genco discuss him, it seems like Genco's voice is dubbed by someone else. His voice sounds very different when he talks in English. Another scene is the flute scene, where the father's voice also sounds dubbed, and 'too Italian'. Is this their real voices, or were they dubbed over?

yeah sometimes you cant even tell its dubbed and sometimes its just to obvious

Not all voices or sound are dubbed. Only about 73% of a films overall sound is dubbed...



noledge

I don't know about the guy who played Agostino Coppola, but I'm sure Genco's voice is that of the actor who played him, Frank Sivero, because Sivero was a major supporting actor in "Goodfellas" and his voice, in English and Italian, is recognizable in GFII. As Tony, Alx and Noledge point out, it's not unusual to use the actors to overdub their parts during post production if the director or second unit chief isn't satisfied with how they sounded on the original soundtrack. I believe it's very unusual to use another person to overdub their voices, except if the original actor is playing a singer and can't really sing.
[Footnote: The best Don Corleone imitation I ever heard was done by Anthony Hopkins, who showed his stuff on A&E's "Biography" of Brando. It didn't surprise me that he was so good: When "Spartacus" was revived and remastered, they restored a scene that had been cut from the original theatrical release showing Laurence Olivier and Tony Curtis in a Roman bath. The Olivier soundtrack was messed up, so they got Hopkins to overdub his voice--perfectly!]