I just finished reading the book, so while i still have a crisp memory of the characters. Here's my fantasy cast:

Don Aprile - Al Pacino
Astorre - David Fumero (not too sure)
Nicole - Kirstie Alley
Rosie - Cameron Diaz
Cilke - Edward Norton
Aspinela - That black girl from "Pulp Fiction"

I would probably go out and hold an audition to find people who fit the description rather than find it through mainstream actors.