CX can price this as a through fare and set its own rate as it flies both segments. It likely is also matching Phillipian Airlines, which offers a lower fare. AC must use a non-partner carrier, and thus create a joint fare, as no STAR airlines operate out of HKG to MNL, thus factoring whatever the joint fare will be. STAR serves MNL via SIN and BKK, so you could fly TG or SQ and connect in one of those two cities. [Not sure if OZ serves it from ICN, you could fly AC to ICN, then OZ into MNL.] Also, CX is pricing this as a Hidden City fare, as their YYZ-HKG fare in the same class is likely as high as AC's. AC cannot afford to lose money flying you in J to HKG, and then give half the proceeds to a competing airline [CX or Phillipines] to get you from HKG to MNL.