I have a similar question as well.
I flew recently from YVR (AC)>NRT (short layover, NH) >SIN (4 day stopover, SQ)>SGN on Y.
I had one check-in luggage.
I also have TD & CIBC Aeroplan Infinite Visas.
When I arrived at SIN (SQ) counter to check in my 1 luggage, they said my Aeroplan booking does not come with free check-in luggage thus I had to pay ~$67 sgd.
I flew back to YVR on Y as well via QH & AC) and there was no charge for my 1 luggage.
I am pretty sure I have flown internationally on Y using Aeroplan and there was never a charge to check in luggage.