Thousand Islands cruise: From pirates and bootleggers to PMs and presidents

"We are now in American waters," says the voice over the boat's public address system, a nugget of information that momentarily, instinctively, sparks a mild flutter of panic. I'm not carrying my passport. Nor do I have an ESTA. But no worries. We won't be raided by immigration. Documents, we're assured, are not necessary for this pleasure cruise around the Thousand Islands, a ravishingly scenic archipelago (of about 1800 islands) in the St Lawrence River, scattered either side of the US-Canadian border, between Ontario and New York State.

On our eight-day tour of Eastern Canada with Collette, we'd hopped on a modern two-tiered vessel in Rockport, a quaint riverside port village in Ontario, and a gateway to a rustic-chic region that has been luring elite holidaymakers since the late 19th century with the promise of fresh air, wilderness and serenity away from the Big Apple, Chicago, Toronto and the like.

While many of the Thousand-plus Islands remain uninhabited, bare slabs of granite or the lushly wooded preserves of racoons and turtles, butterflies and migratory birds, others boast clapboard holiday homes, whimsical mansions, boathouses, golf courses, ruined forts from the American Revolutionary War, traces of ancient campsites of the indigenous First Nations people, and poles with fluttering flags, sporting stars and stripes and maple leaves, depending on which side of the border they nestle.

We pass kayakers and fishermen, and spot the occasional hulking freighter (it's estimated that 50 million tonnes of cargo are shipped annually along the river, part of the Saint Lawrence Seaway that links the Great Lakes with the North Atlantic Ocean).

You could easily switch off, gazing through the windows at this dreamy waterscape – perhaps imagining yourself lolling in a bankside hammock, or zipping around in an ostentatious yacht, Wolf of Wall Street-style. But the boat's audio commentary is worth a listen, infused with absorbing tales about the characters who've left their mark here, from pirates and prohibition bootleggers to prime ministers, presidents and tycoons. We're approaching Deer Island now.

At first glance, there's nothing special about it. But beyond its thickets of pine, oak and maple trees lies the country lodge of the Skull and Bones, a secret society at Yale University that is said to count George W. Bush and John Kerry among its alumni. Images of mysterious masked rituals around the campfire drift through my head, but perhaps it's because of The Skulls. Scenes from this 2000 movie – an outlandish thriller inspired by conspiracy theories surrounding the Bonesmen – were, we hear, shot on Dark Island.

About 10 kilometres upstream from Deer Island, it's home to Singer Castle, a fanciful property inspired by the castle in Sir Walter Scott's historical 1832 novel, Woodstock. We don't see that today, but we do cast eyes on another flamboyant pile: Boldt Castle. Resembling a fairy-tale European chateau with its riot of ornate stone, spires and turrets, it's on Heart Island, and was commissioned by George C. Boldt, the German-born owner of New York's Waldorf Astoria Hotel, as a gift, and summer retreat, to his beloved wife, Louise. After she died suddenly in 1904, a devastated Boldt ordered an end to the construction and the castle stood unfinished for more than 70 years, gnawed at by the elements and attacked by vandals.