Some recent data points from Northern Ontario:
January 26
YQT-YYZ-YXU
Booked in Flex (U) for $527
J9 at OLCI
LMU offer - $82
January 29
YQT-YYZ
Booked in Standard (U) for $390
J7 at OLCI
LMU offer - $129
January 29
YQT-YYZ-YXU (same flight to YYZ as above)
Booked in Flex (K) for $199
J7 at OLCI
LMU offer - $151
January 29
YQT-YYZ-YQG
Booked in Business Lowest (P/M) for $386
OLCI doesn't open for another 5 hours, but currently it's J9 with 4/12 seats taken
.
Looks to me like the LMU price correlates best with the price of the ticket rather than the fare bucket or type (e.g. Standard U is less than Flex K). I'm not sure if the Flex U is cheaper than the Standard U because of the fare type or because it's J9 vs. J7.
In any case, a cheap Flex fare + LMU works out to $350, which is not a whole lot less than the cheap Business Lowest at $386.