My 2c, I think this is Rouge, and the rest of Y would be awful all the way to PHX, so I would check to see if I could pay the upcharge for seat selection in the front row of Y as a backup plan, and if there seems to be a reasonable amount of unsold J, ask Air Canada for the incremental cost of booking H class (or U or M) where the eUp would require only 8, not 15.
If J is already looking full, then I would leave it in the lower flex class and give up that hope.

Those who know about booking classes would have checked the eUp requirements and if we only had 14 credits and wanted to upgrade this flight, would have booked H to start with. It is almost unfair to expect people to have the ESP to know this is something they should check. Most non FT people think Flex = Flex = Flex. When people receive their Elite kits for the first time, they really should get some briefing on this, instead of vague language that tells them they can look up upgrade credit requirements on the internet.