I am a US citizen travling to Venice, Italy with a connecting flight in Canada. Do I need a travel visa or other documentationto pass through Canada?
Your US passport is all you need. No visas or anything are needed for a US citizen to enter Canada for transit or visiting. You don't even need an eTA, which most other nationalities do.
You do not need a Canadian passport, a Canadian visa or an eTA to enter Canada if you are travelling with a valid U.S. passport.
Have a nice trip!