I travel YYZ to HKG quite a bit. Lately
AC 15 shows no R class available. There can be 15 J class seats available but they won't give them out till the flight closes. If you want to book AC 007 that takes an extra 5 hours then you can upgrade in advance.
On the 24th AC 016 shows 33 seat available in J but R is 0
On AC 008 has 27 J and R9!
Why do they make us play the game?
On CX you can confirm well in advance.