For What I know, to use $200 travel credit (CAD), you actually have to book through AMEX travel agencies... so like "jerryhung" said, you will be starting from published fare and get the reimbursement from AMEX when you call. I had to ask and book through the amex travel agency to get the credit for my flight to Korea.
So for any deals outside of AMEX or published fare, that are between loyalty programs, we are out of luck...