Castrogiovanni, who is making his 87th appearance, will lead the Azzurri for the first time with skipper Sergio Parisse and vice-captain Marco Bortolami both out of action after getting hurt in last weekend's 37-22 defeat to Argentina in San Juan.
"I am enthusiastic and a little bit nervous," Castrogiovanni said to www.federugby.it. "But I know my team-mates will help me out in this new role and will give me their support and understanding.
"We have to focus on our game because if we make the mistakes we did against Argentina then we can lose against Canada."
Italy have won their last three meetings with Canada but know a defeat could see Canada leapfrog them into 12th in the world rankings - Canada are one place below the Azzurri.
Jaques Brunel's Italy expect a very hard game.
"Canada are a very physical side," Castrogiovanni said.
"They proved in the last World Cup they can win against anyone and they will be eager to come out victorious in front of their home fans.
"They are very organised defensively and for that reason it will be crucial for us to maintain possession and to throw the ball into touch whenever necessary."
Canada coach Kieran Crowley has made six changes to the side that beat the United States 28-25 in Kingston last weekend.
Among those changes is hooker Mike Pletch, who will replace injured Ryan Hamilton, while tighthead prop Jason Marshall is returning to the starting XV.
Crowley was pleased with his team's performance against the USA Eagles but is aware his side faces a bigger battle against Italy.
Canada's last victory against the Azzurri dates back to November 2000.
"Italy will be a lot stronger than the USA," Crowley said. "We will not get away with the mistakes we made last week.
"Cutting out the errors in our game is the big focus for us, and if we can improve our continuity then the points will come."
Brunel will hand uncapped players Aironi full-back Alberto Benettin and Treviso centre Andrea Pratichetti their first appearances, while scrum-half Tito Tebaldi returns to play in the Azzurri colours after a two-year absence.
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