Frank White's last post raised a question I had not considered until now: did the rest of the Corleone's ever know that Michael was married in Sicily? I would assume so through Don Tomassino. Maybe Mama never knew that Michael was married and her advice to Kay in the novel was because Mama truly believed Michael murdered McCluskey and Sollozzo.
Don Tomassino, as Michael's protector, had to have reported his interest in Apollonia. If the Corleones objected, Don Tomassino probably would have tried to nip the courtship in the bud--perhaps even arranging for Apollonia to leave Sicily. But I'm sure the Corleones approved enthusisastically--Michael was going to marry a real Sicilian girl, not a "washed-out rag of an American girl," as the novel put it. (BTW: in a deleted scene from GF, Vito asks Michael after Connie's wedding: "Did your American girlfriend get home all right?", then rolls his eyes contemptuously. Note how Kay never appears in any scenes with Vito except in the family photos at the wedding--and at his funeral.)
Did the Barzini's and other Corleone enemies know that Michael was married or was the car bomb meant exclusively for Michael, with Apollonia being an accidental victim? Again, I would presume it was no secret to his enemies and that they could have found out when Fabrizzio turned traitor.
The enemies had to know that Michael was married because his wedding was a public event for the entire town of Corleone. Just as Vito had allies in Sicily, so did Barzini and probably the other Dons. It would have been easy for them to probe for a ch**k in Don Tomassino's armor, and to recruit Fabrizio.
I doubt that Barzini, through Fabrizio, intended to harm Apollonia--but, like Roth's attack on Michael's bedroom in II: too bad if someone got in the way.
