MAD-YYZ should be operated always 3xw during W09/10, without stopping @ YUL (as far as I can see through AC.com).
Both destinations, MAD & FCO, were axed during W08/09 due to the rising cost of fuel and falling demand. Then YYZ-FCO has been restabilshed in Mar 09 while YYZ-MAD 2 months later in May 09. FCO will also get a new dedicated service to YUL for the summer.
But I guess there is not enough p2p traffic between Quebec and MAD (like to FCO or GVA for example) to justify a YUL stopover on the YYZ-MAD route.