John Cabot had a first landing site of the province that blocks the mouth of what river?
John Cabot:  To mark the celebration of the 500th anniversary of Cabot's expedition, both the Canadian and British governments elected Cape Bonavista, Newfoundland, as Cabot's first landing site. Newfoundland (island):  It blocks the mouth of the Saint Lawrence River, creating the Gulf of Saint Lawrence, the world's largest estuary.
Saint Lawrence