Since you are from Canada, If you have enough miles in your AC account, you should be able to book a stopover at Narita, and you still have a openjaw to use.
But for people from Europe, then stopover at Narita may not be allowed since the stopover rule defines the point to stopover can not be farther than the destination.
But for people from Europe, then stopover at Narita may not be allowed since the stopover rule defines the point to stopover can not be farther than the destination.