Hi I was originally planned flying from Brisbane to Chicago via YVR end of the year on AC but because of some circumstances I have to delay my travel by few days.

So I'm looking at the ticket price right now and the price I paid for my ticket is already insanely expensive and now if I want to change to few days later AC wants to charge me another 1.2k which I definitely don't want to pay.
Then I realised if I change the ticket to YVR only, and buy a separate YVR-ORD ticket I only have to pay $200 more which I'm ok with.

Given both tickets are with the same airline normally there wouldn't be any issues with checking my bags all the way to destination but because this is my first ever time transferring and pre-clearing US customs in YVR I'm not sure whether this would encounter any issues. (also I'm entering US on J1 visa)

I tried to google it but couldn't find any similar answers.

Any help is appreciated.