With no *A connectivity between LHR and the regions, MAN included, regional bookings have fallen off a cliff for those carriers.
I believe that 2 carriers currently being courted are Air New Zealand once again, who may move the LHR - HKG - AKL to MAN, and China A/L with a MAN-BKK-TPE.
Doubt you are going to poach ANZ's second LHR flight given that the comparable point to point traffic volumes are not similar. However bear in mind
Air Canada still operate a summer service to Dublin, Barcelona and Rome, if any STAR carrier was going to relaunch long haul, they might be the best bet on MAN-YYZ.