I'm taking a flight on an Air Canada Codeshare (ANA Operated) flight from HND to YVR to transit to YEG, and want to purchase duty free liquids from HND.

Given the FAQ at the top, am I correct to assume that because I am flying ANA operated flight (despite it being AC code share) and my onward connection is AC metal to YEG on the same itinerary, that I will still have to go downstairs to the big customs hall and grab my luggage, exit to landside, and re-check my bag at the check-in counter on landside? My issue is getting a CATSA agent that doesn't understand that STEB bags from duty free stores are accepted and allowed to be carry-on when transiting and having it confisicated, so if I can confirm that I will be forced to grab my luggage at YVR regardless, then I can safely purchase liquids in HND and re-check it in the luggage.