Expert flyer shows 16 unassigned seats in J, which is a lot, and makes me wonder who are those 9 people who bought seats but didn't get seat assignments.

The AC web site says you'll be wait listed. Look up a one-way trip YUL-FRA on that date, even if you say you're E100 and pay a Latitude fare, they'll still wait list you. So bring that pillow for your Y seat.