Google Flights is directing me to aa.com to purchase a flight US-Europe in J all on AA metal, but the outbound is an AY flight number operated by AA ($1,500 cheaper than if I book the AA flight number).

As EXP/OWE, which of my benefits will I still have on the AY marketed flight? Most concerned about advance seat selection and baggage limits.

So many common search terms that I couldn't find an appropriate thread.

Thanks!