This outbound is likely valid, as anything via SIN seems to be valid:

Sun Dec.01 YVR-YYZ 08:00-15:28 AC142 pods
Sun Dec.01 YYZ-WAW 18:20-08:40+1 LO2 788 flat beds
A day in Warsaw
Tue Dec.03 WAW-ZRH 07:25-09:30 LO411
Stopover in Zurich
Tue Dec.10 ZRH-SIN 22:45-18:00+1 LX178 flat beds
Thu Dec.12 SIN-PER 01:05-06:20 SQ225
Perth

Return:
PER-SIN-HKG is available almost any day.
HKG-YVR on AC - no availability. Maybe another routing will work, like HKG-ICN-YVR.

If you want Melbourne, you will need to buy a separate return ticket PER-MEL. Or, remove a stopover in Zurich, and make an open jaw, returning MEL-SIN-HKG-ICN-YVR (if allowed), but I wouldn't do it, because removing a stopover in ZRH makes a very very long and tiring flight YVR-YYZ-WAW-ZRH-SIN-PER without stopover.