Originally Posted by jrobin

Two thoughts:
1. if you are really just visiting YYZ, and not YUL for an extended period, you could change the YUL-DFW to YYZ-DFW with no need to return to YUL.
2. If/when you call AA, they may request use of an AA codeshare for long flights like DFW-TYO, but with your use of AA for DFW-GRU return I suspect AA will be willing to use your itinerary as posted. You can always call AA again if you want to tweak the itinerary after getting a price on the first draft,