Originally Posted by Tedgrrrr

Yes, but still, try to book Z if it's not that much more. Also, I'm not sure how many daily flights there are out of YUL, but you may be better off doing YYZ-YUL-LHR, because connecting pax get priority that may even trump fare class (though no one knows for sure). Of course, you're probably better off on a 777 from YYZ, than on a 767 from YUL, just because there are so many more seats on 777. But if you can find a 777 from YUL, then with M class + connection = great shot at upgrade.