That's wierd. Heavy cargo just on that day? But don't passengers have higher priority than cargo?
NO CX has the wrong planes a 777-300 does not really have the range thats why AC uses the 777-200 LR. CX plane has more J and F seats and they would reduce weight.
However YYZ-HKG is the "longer" route and even more weight restrictions would be needed.
Interesting that CX didnt buy the 777-200lr?