I think it was orginally scheduled to start at the beginning of May, but they decided to postpone the start of the summer service until June. I think that people who were booked to travel in May have been rebooked via LHR.
It's still bookable on Air Canada's website etc.
They have got a bit of extra competition with Zoom now operating and TCX being daily during July and August, but hopefully there should be enough of a market for all of them.