Busan, South Korea is a relatively tricky city to reach using Aeroplan (or any Star Alliance miles, for that matter) – especially relative to its size. Unlike Korean Air, Asiana does not operate domestic flights from Seoul-Gimpo to Busan, but instead does so via its subsidiary Air Busan which is not a Star Alliance partner (so no Aeroplan redemptions are available). Asiana Airlines has a few point-to-point routes out of Busan, including Guangzhou and Manila, and Thai Airways operates Bangkok to Busan on a regionally configured Boeing 777-300. Both of these options would normally incur fuel surcharges, making them less than ideal. Asiana however operates special Seoul-Incheon to Busan shuttle flights which are available for award booking.
Asiana Airlines flights from Seoul-Incheon to Busan are not bookable as a stand-alone flight but must be booked as part of a connecting itinerary through Seoul-Incheon. The connecting flight however, does not have to be on Asiana, and as there is no fuel surcharge on a domestic segment, you can completely avoid fuel surcharges by booking either United, Singapore Airlines or EVA Air to Seoul-Incheon then connecting onwards to Busan.
Transiting in Seoul-Incheon
Unlike a traditional international to domestic connection, Seoul-Incheon to Busan flights are considered an international connection – therefore you do not clear immigration in Seoul-Incheon. Instead, you will need to head to the Busan transit counter for an airside transit. The Seoul-Incheon to Busan leg is considered an international flight and all arriving passengers disembark at the international terminal in Busan and must complete immigration and customs processions there.
If you have an extended layover in Seoul-Incheon, you must clear immigration to enter South Korea, but then check-in and clear immigration/customs for the Seoul-Incheon to Busan flight as with any other international flight, even though it is operating on a domestic route.