Upvote:2
I would use the Brazilian passport to board the plane, and then use the Australian passport at immigration. I have been in the same situation, I booked a flight to Italy with my Aussie passport, but when I got there I used my Italian passport just fine. Iām not sure if you have to show evidence of a Visa to check-in staff, or if showing them your Aussie passport is enough, I would call the airline about that.