A crowd of more than 12,000 saw Italy dominate at the set-piece, allowing fly-half Kristopher Burton to keep Italy in control of the scoreboard at BMO Field.
The Canadians, with seven British-based players in their line-up, led with a James Pritchard penalty before the tourists established a platform and pulled away with six penalties from Burton and a try from hooker Tommaso D’Appice to give Castrogiovanni a winning start as skipper.
Castro's Leicester Tigers front-row colleague Logovi'i Mulipola is also in international action this weekend after being selected at tighthead prop for Samoa in Sunday's Pacific Nations Cup match against Japan.
Following victories over Fiji and Tonga, the Samoans can pick up a second PNC title by avoiding defeat in their round three match against the tournament hosts.
Steve Mafi's Tonga conclude their championship against Fiji next weekend.