In my opinion, upgrading with miles isn't worth it. It's 25,000 miles + $350 each way, and you won't be able to upgrade the NRT-CGK leg (a 6hr flight). I would use your miles for an award--and buy the 20K miles if you want J both ways (there's a promo at the moment).

Also, note that AY has great J fares from YYZ to certain Asian markets. For example, YYZ-SIN is $2,589, and you could buy cheap tickets connecting ORD and YYZ, and SIN and CGK.