When Frank Gio shoots the young druggie in the Brooklyn Italian restaurant, the final slow motion shot of the druggie tumbling to the ground reveals plainly obvious squib wires running up his pants leg.
This film has absolutely nothing to do with Corleone, with most of its first act is set in Palermo (also in Sicily but a distinctly different city). The only mention of Corleone is that it was where minor character Giuseppe Caruso was born and he has nothing to do with any trip to Brooklyn.
The main characters travel from Palermo (which is on the island of Sicily) to Rome via driving and a aboard train, with no mention of them having to take a boat across the Straights of Messina.