I was in a reverse situation about 11-12 yrs ago.

I was supposed to fly on Canadian Airlines (CP) - it was independent airline, separate from AC at that time - and I was booked to fly from LHR to YYZ (onwards to YOW) - but due to mechanical problems of the CP plane, the CP flight was cancelled, and I was re-booked to go on AC on this route. (note-CP was a member of One World at that time, AC then and now is/was a member of Star Alliance).

I later communicated to Canadian Plus, the frequent flyer arm of CP, and I received those Canadian Plus miles.