I think AC is just too expensive to make a pure MR ever feasible. The best you can really hope for is to add a stopovere on a business trip. i've started flying LHR-YUL via Toronto in part for the extra 1600 miles (and to get XM aircraft) for example.

If there ever was a MR available I think what you would have to watch out for is a route that westjet flies where westjet put n a promotion and AC matched it but without tweaking their routing rules. If it happend it would probably be something like YYC-YUL via YHZ or something like that.

Even then as the other poster said they would probably only match it with a T fare. You need them to do a T+ fare to earn miles. Assumin you're accumulating with AP. A UA MR on AC might be possible with T fares, not sure.