Upvote:3
Canada has preclearance for customs & immigration for US bound flights so you are treated as a domestic passenger when you arrive at LAX. Bags should just transfer fine, just like any domestic connection. I flew through Auckland in Feb of 2020 on an international itinerary (SFO -> AKL -> MEL) and I did not have to do anything with my bag. In fact, I left the airport completely for several hours. Obviously check with the agents if you have any confusion since it would be unfortunate that your bags are circling a carousel 3 stops back. I'm also not sure how COVID changes immigration/transfer policies, you may want to check that as well.
Upvote:9
Each country has different rules. The US does not have the concept of "transit passenger" and you will have to enter the US by going through immigration and customs. However, from Vancouver this is done at "preclearance" which means you will be a domestic arrival in LAX and will not have to go through immigration at all there.
In Auckland, you do not have to enter NZ (that would currently require quarantine for COVID-19), so your bags may be checked through to Brisbane. In that case you would only need to hang around in the transit area until your next flight leaves.
The best advice is to ask the at the check-in counter when you check in. They will be able to tell you.