Originally Posted by warrens

100K Aeroplan points probably get you one Premium Economy seat in one direction from Vancouver to Seoul Incheon. These are desired routes so it doesn't come cheap. If you want business seats, be prepared to pay.

My suggestion to you is this -- do a round-trip to Seoul, then put together a separate itinerary for Korea -> Japan. It doesn't have to be a round-trip flight.... you could fly to Osaka, take the shinkansen to Tokyo, then fly back to Seoul from Haneda. (If you do this, try to avoid flying through Incheon and Narita and these airports are a long ways from the cities they serve.). You can get business class tickets from Seoul to Osaka or Tokyo for around 20,000 Aeroplan points most days, and the service quality is exceptional. Yes, you can book flights between Korea and Japan with Aeroplan! Use the Air Canada web site to do it.

The main reason to fly to Seoul instead of Tokyo has to do with demand. People are clamouring to go to Japan in large numbers and the prices & availability will reflect this. People are literally buying tickets for one year to the day, as soon as they become available. Korea is popular, too, but nowhere near as much so.

I will also assert that entering Japan via Osaka International (KIX) is more pleasant than either Tokyo airport due to shorter lines at passport control.