Who knows. I wonder whether the YYC-NRT route will just die. It was run with 788 at times in the past, but even that's a significant upgauge from 763 - about 20% more seats (255 vs 211 total, albeit 4 fewer J seats in the 788). Unlike some other routes that AC has introduced in recent years, which started as seasonal and/or less-than-daily frequency and then grew, YYC-NRT has never really caught fire, just sort of limped on.

It may be that it makes just enough money to fly with a 763 but isn't profitable with anything else.