Customs and Immigration in Toronto

I am guessing you connect with your next flight in Toronto as you would any other flight, find the next gate and head over. I assume your checked luggage would transfer to your next flight and that the Canadians would not make you essentially leave their airport and re-enter. A call to your airline would definitely advise you one way or another.
Enjoy Rome and your short hold over in wonderful Toronto.

In which terminal(s) are you connecting?

Sorry forgot to give key info. It's Air Canada all the way from Chicago/Toronto/Rome. Arrive and leave Toronto Airport from Terminal 1. I have gotten conflicting information about the customs and immigration.

Hi Bobbie. We did a similar trip last year from Minneapolis via Montreal. Yes, we did go through passport control in Montreal. And even though our bags were supposedly booked all the way to Europe, we had to pick them up and recheck in Montreal. We foudn Air Canada to be a pleasant airline; enjoy your trip!

My experience was similar to Bob's. We had to go through passport control. We carried our bags with us, so no need to pick up and recheck them. Air Canada was pretty nice. With dinner they gave us each a small bottle of wine. I was surprised, as we were sitting in the cheap seats!

Hi Bobbie, Here is a link to the info on the airport's website. Yes, you will need to clear customs here. Happy travels. http://www.gtaa.com/en/travellers/connecting/connection_tips/

I have heard on other travel forums that when going through Toronto, unlike other international terminals, you must go through immigration, claim your checked baggage, clear customs, then check in for your connecting flight.

going to europe via torondo is easy - canadian custom officials are pretty easy on US passport. you do go through Italian's passport control when you land, but it's usually just line, no question asked. on your way back you'll likely suffer at the US custom in Toronto - get your luggage, get through the lines, and being questioned, then drop you luggage off. this is where you likely will miss your connection if a short layover, so you want to move as quickly as you can. air canada is nice enough some times will hold the flight for extended 30-40 min - they see the pain travellers suffer at the US custom on a daily basis.