Unfortunately YYZ does not offer a "sterile" international transit facility and in most cases, international-to-international connecting passengers will have to go through Canadian immigration and custom formalities. For further information, I suggest to go to the airport web site at www.gtaa.com and there is a function to send the GTAA an enquiry with your arrival and departure flights for an official guidance. Both CX and AA operate out of T1 so at least you do not have to change terminal!