Agree that not all connections to the US at Toronto can be made without Canadian Border Controls. But AC connections at Terminal 1 are the exception.
From the
AC website:
International flight to the U.S. - connecting through Toronto
Take the escalator down one level and turn immediately left. You are not required to clear Canada Customs and Immigration formalities when connecting to the U.S. However, you must still meet all entry regulations set by Canada Customs and Immigration, including any transit visa requirements.
Take the escalator up one level to the U.S. Connection Hall and pick up your baggage (have bag tag receipts ready for presentation prior to entering the U.S. Customs Hall). To make your travel experience as seamless as possible, complimentary luggage carts are provided at the baggage claim area. Ensure all duty-free purchases containing liquids and gels are placed in checked baggage. Have all documentation in hand and ensure all applicable forms have been completed. Proceed to U.S. Customs and Immigration and drop off checked baggage. Continue through Security to your departure gate.
Most Europeans do not need a visa (or a visa waiver) to enter/transit Canada.