I traveled in June this year from Germany to US through Toronto (AC flight). I did not have to re-check my luggage (in fact this is why I did chose this flight). Yesterday, I flew again, but this time my luggage is still Toronto - I was told by the employee at the US airport that I should have re-checked my luggage.
Were there some recent changes in the policy?
Update: My luggage was delivered two days later, unopened.