Interestingly the fare rules don't show MIA as a valid routing for a through fare. Not sure why you'd get options via MIA. Are these offered on AC.com or on an OTA? If the latter, then it might not be an AC ticket.
/WITHIN THE WESTERN HEMISPHERE/
MAP CONSTRUCTED LEFT TO RIGHT AND RIGHT TO LEFT
1. BHZ-AC-RIO/SAO-YTO
2. BHZ-AC-SAO-YTO
3. BHZ-AC/CM-PTY-YTO
4. BHZ-AC/G3-RIO/SAO-YTO
5. BHZ-AC/G3-SAO-YTO
6. BHZ-G3/JJ-RIO/SAO-YTO
7. BHZ-G3/JJ-SAO-YTO