250,000 seats is a massive number - I reckon it's the equivalent of four fully laden A300 flights every day throughout the summer season (and they have four A300s which don't work that hard). A little bit of 757 flying to Canada is not going to come close to making up that shortfall in activity across the whole fleet. Are the A300s about to disappear?
The article says Cosmos and other independents will take up most of the capacity, so Im not sure there will be much of a shortfall in activity