Transfer itinerary might be difficult to find. If you break the sectors by searching for a multi-city for MIA-YYZ and YYZ-GRU, it shows up but the cost goes up due to routing (less than 24 hour stopover doesn't incur additional miles in general). Usually Asiana sees the same X class inventory with the others but looks like copa PTY-GRU isn't showing up on Asiana for some reason.