I didn't take checked baggage many times with CP (and always with AC), but my experience since getting priority tag status is that CP and AA consistently did a lousy job of giving my bag priority, i.e. they didn't, and AC consistently had my bag out early.
Airports are YOW, YVR, YYZ, and LAX for CP/AA, and YOW, YYZ, LAX for AC.
andrew