I would fly AC J for two main reasons.
Fully flat seats in AC J are way more comfortable on a long haul flight that any variety of traditional seat (JL Y+). Soft product may be better with JAL being an asian carrier with typical asian carrier (excellent) service but YMMV.
AC's little publicized stopover program for business class and full fare Y pax.
Link here. AC will pay for a hotel room for you for international connections over 6 hours. I would take that opportunity to spend some time in Canada's biggest city and see some other sights.
But then again, best schedule may prevail over all if time is precious.