Checking the rules on the CX website - https://www.cathaypacific.com/cx/en_....html?switch=Y

IATA tariff area 1
North America, Central America, South America and Hawaii

Sub-tariff areas in tariff area 1
USA, Canada, Mexico, Caribbean, Central America, South America

Your most significant carrier is defined as follows:
- If your flight travels across an IATA tariff area then the first carrier that crosses a tariff area is your most significant carrier

- If your flight does not cross an IATA tariff area, but travels across a sub-tariff area then the first carrier that crosses the sub-tariff area is your most significant carrier

- If your flight crosses no IATA areas, but crosses an international border then the first carrier that crosses the international border is your most significant carrier

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Since the 1st leg (Air Canada YVR-YYZ) does not fall under the 3 definitions, then does that make the 2nd leg (CX JFK-YVR) as the most significant carrier as it is the first flight to cross the international border? Or am I clutching at straws here 