What would be the contractual basis for your result?

Both the International Tariff (Rule 60) and the Domestic Tariff (Rule 65) state this: "Additional baggage pieces outside the regular baggage allowance set out above are only subject to one excess baggage fee, even if the baggage is also overweight and/or oversize."

So one could argue that the ticket, being a ticket to SYD, falls under the International Tariff, so the fee is CAD 225 +tx. I argue that the oversize/third item only travels within Canada, so the fee is CAD 100 +tx.

But in either case, the total cost doesn't change if 0, 1, or 2 normal bags are checked, as along as there is one oversize item. The charge would be the same, wouldn't it?