How do I get status and credit card benefits if I book a flight itinerary where some of the flights are operated by a different carriers ?

For example, if I book a flight itinerary on United, and it includes a segment operated by Air Canada under a United codeshare, will I be able to get my Air Canada status benefits, such as priority boarding ? I don’t have status with United, but I would still need to use my United MileagePlus account number when making the reservation, to get some benefits from my United credit card.

Another scenario is making a reservation on AC, which includes a segment operated by United. How will I receive my United benefits, such as priority boarding and economy plus seat, if I make the reservation with my AP account ?

I don’t understand how this works when there are multiple carriers involved in the itinerary, so I would appreciate it if anyone can explain how this works.