That's fine. Do you need to go to YYZ for any specific reason? You might also consider YVR for extra miles and more time to enjoy the F service. YVR is a great city, particularly in the summer. The rest of the year its cool and rainy, but will still be lots warmer than YYZ... I think AA flies YVR-ORD in the summer, if not, you can do YVR-DFW and sub DFW for ORD.

You might also consider dropping the LAS-LAX leg since it's Eagle on a regional jet (all-coach), and purchase that separately, either on AA or any other airline, that would free up another N. Amer segment for you to maximize mileage and service. So maybe LHR-YVR-DFW-ORD-LAS, LAX-MIA...

Then, consider substituting GIG (Rio) for GRU, there is a 1-stop direct JFK-GIG, and I assume LA will fly GIG-SCL (If not, then stick with GRU or purchase GIG-GRU separately). GIG is much more of a tourist destination than GRU. Alternatively, EZE is a really great tourist city. No F service on JFK-EZE, but you can tweak your routing: ...LAX-JFK-MIA-EZE-SCL... You'd probably lose some miles vs. the GRU/GIG option, but that should be omre than made up by flying your N.Amer. transcon on LAX-JFK in 3-class "flagship" service, which will be much better than LAX-MIA, even if you get on the 763 on that route. Good chance of seeing a celebrity too...

See, I told you we could be more helpful if you did your homework first!