Originally Posted by lowside67

The simple answer is this:

For each city pairing, there is an "MPM5" value which is the absolute maximum that you can use each direction to get there. Some city-pairs such as YYC-SYD have one value which requires to transit only across one ocean, Pacific in that case, and some city pairs such as YYC-SIN have two values depending on which ocean you are crossing.

The bottom line is that the YYC-SYD value is only 10,316 miles (the YYC-AKL value is even less at 9xxx miles) so this will be your limiting factor. If there is another published routing to get there, you can take that as well even if it's over that, but if you want to "design your own", then you have to stay within that value.

YYC-NRT-AKL-SYD is over this value but if you can find a carrier that would suggest that route if you put in YYC-SYD, then this should be doable. However, I think you will have a hard time not finding a routing that involves an AC YVR-SYD leg.

Edit - what are your desired dates?

Mark