Leaving aside error fares, it's quite hard to earn AC metal SQM at a cost lower than $0.07CAD/mile these days, which would translate to $70k to earn MM status.
PE (N) fares YYZ/YUL-TPE/HKG are probably among the fares with the best cpm, earning ~20000 SQM and costing $1300-$1700CAD a.i. r/t.
Occasionally, there are some reasonably priced PE fares ex-Europe that would also offer a <10cpm earning. (E.g. ATH-YYZ-YVR-LAX r/t in N for <$1500CAD a.i.)