At the gate SE's will get first crack at any seats that come available. Once they're all accommodated, the E75's come next. If there are any seats left after all E75s have been accommodated, they will look to E50's.

This is a fair system. If someone flies 100k a year (or moreso, 95+ segments) they deserve all the breaks they can get.

Not sure about YUL-FRA ....... on the YYZ-FRA flights I've done, it was usually a case of 10 SEs fighting it out for 2 or maybe 3 available seats. Of course, your mileage will vary.