A great fresh-water summer cruising destination, the Thousand Islands dot the St. Lawrence River between New York State and the province of Ontario, straddling the invisible border between the U.S. and Canada. It’s an area where you could easily spend a few days, or an entire summer, navigating – slowly – among the granite islands that have been there since the Ice Age. Some are large, generally meaning a few acres, and some are small; one is the size of a billiard table. Large or small, the rocks surrounding them are real; you definitely want to stay in the well-marked…