Originally Posted by AJA_

Radtel Are the FNC -LHR and the LHR-YVC flights on one PNR or did you book the FNC flights separately?

If on one PNR I would wait a few days as BA's systems should pick up on the misconnect for the later transatlantic flight and either rebook that the following day or offer you an earlier option for the FNC-LHR flight.

If on separate bookings you need to contact BA and request an earlier FNC departure, possibly the day before, as you will be marked as a no show for the transatlantic flight if you do nothing. You will not be able to change the transatlantic flight unless there is reward seat availability.