I never heard that Michael was modeled on Bill Bonanno, but I can understand why some might think so. The Bonanno parallel is that, until John Gotti tried to foist his son on the Gambinos, Bill Bonanno was the only NY area son who was intended to succeed his father. The irony is that Bill was acting boss of a family faction while his father was in exile, while Sonny was the acting boss when Michael was in exile.