Thanks for all the detailed info about pre-clearance etc out of Toronto.......but what happens on the way home (to Toronto) flying AA via CLT? Do we have to collect our luggage, clear customs and recheck to Toronto? or our Canadian bound pax except? Any info is much appreciated.

Done this route many times but not recently. As I recall:
Check in SXM, get both boarding passes and bags tagged YYZ.
Arrive CLT, clear US Immigration (separate and slower line for non US citizens).
Pick up bags and drag past US Customs.
Throw bags on to another conveyor.
As you will have left secure area, you must go through security again to reach your gate for flight to YYZ.

Something I just thought of in this situation. Not sure if you plan on bringing back anything, but beware you can only claim your $800 per person exemption once every 30 days. So, I'm not sure how declaring anything you have in CLT would impact your arriving again in the US on your way home after leaving YYZ.