I don't think I will have a boarding pass for the LAX-NAN leg in my possession. I believe I have to pick that up at the Fiji Air counter in Terminal B. I'm wondering if I will be able to walk airside from T6 to TB without a boarding pass? Or would there be checkpoints along the way requesting to see a boarding pass? I think Fiji Air is requiring people to check in at their counter for presentation of documents.
As Phil says, you might want to try to call Air Canada and see what they say.
If you don't get your boarding pass for LAX-NAN when you check in initially in Canada, then yes, you will likely need to exit the terminal and go to the Fiji Airways desk in the departures level in Terminal B and get your boarding pass and then re-clear security.
Given that Air Canada and Fiji Airways are in different alliances (Star Alliance vs OneWorld), that might be the case.
As long as you have time, there are plenty of helpful people (believe it or not) at LAX that can help you get to where you need to go.
- brett