not the same route, but another data point...
Flew AKL - CAN return late last year with CZ. We tried upgrading at check in on outbound but they were charging the full fare difference and advised to ask on-board.
We asked on-board and were able to upgrade J to F for 3000 RMB each - around $480 US each flight.
The lead FA had the prices for each cabin class upgrade written on a piece of scrap paper both times, they ran our credit cards through the machine and moved us up.

We had the 4 F seats for just the 2 of us and a dedicated FA. They still served business class food and drink but we did get full F amenities, including duvet, better pillows, upgraded slippers, amenity kit and pajamas. They also set up snacks and bar service at the front of the cabin.