Westjet have talked about opening MAN too. However they also talked about EDI, so, who knows.
People seem to be focusing on Halifax. Lets not forget, they are using Halifax as a hub/transit point and onwards to Toronto.
While some could argue that MAN-YYZ is now quite busy, with daily Air Transat and an extended season on Air Canada, It all depends on whether Westjet want to compete for onward connections.