Air Transat have operated the EDI flight for at least 14 years, so im guessing its the financial climate thats stopped the flight for 2010. NCL and EXT have also been dropped for 2010. TCX even had a flight for two or three years for Canadian Affair to YYZ.
The TS flight used to be on a B757 and operated non stop, so must have been enough demand, i seem to recall at one point TS had ABZ, EDI, GLA and PIK in the 90s to YYZ.