If you fly SQ to NRT and then a surchargeable carrier from there after a stopover - you should get the lower Japan (government mandated) surcharge.

However, Air Canada has a scam going on top of a scam - they charge surcharges based on the entire route, even if part of it is non-scamchargeble - so you wont know until you try

Either way, it will be $102 change - so it may erase any savings.