Connections through St John`s to onward destinations in North America would be key.
Have you looked at where you can actually connect to from St John's?
In terms of places that people from Cork might want to go, it's only really Toronto, Montreal and New York.
That's why I suggested that if a short route to eastern Canada was to work, Halifax might be a better destination. There at least it's possible to connect to most major cities in the north and east of North America.