According to this:
https://www.aircanada.com/en/traveli...images/yyz.pdf
Which was Jan 31, 2012, AC instructions are to place duty-free in checked bag before continuing to connecting flight.

I will be in a position in a few weeks to buy duty-free on a flight from SFO to YYZ, and then on to YXU, with no checked bag, and don't intend to test the system unless there is something in print *somewhere* that tells me they know how to handle bonded bags.

And if you don't have checked bags, why can't they figure out a way for you to continue airside to a connecting flight after hitting immigration?