Ernest Fenwick MacIntosh arrived in Nepal last August and approached a homeless children centre with the offer of donations where he met the victim, a 9-year-old boy, police said.
The Canadian tourist lured the minor into his rented room at a guest house on December 13 and molested him, police spokesperson Pawan Kumar Giri said.
The boy is said to be from Achham, currently staying at a children's home in Lalitpur, Giri was quoted as saying by the Himalayan Times.
The accused has denied any wrongdoing.
MacIntosh was accused of sexually abusing boys in the 1970s in Cape Breton, an island on the Atlantic coast of North America. The allegations surfaced in 1995, when he was living in India.
But he was not extradited until 2007 and the first of his two trials in Nova Scotia did not start until 2010. His convictions were quashed in April 2013, Canadian newspaper The Globe and Mail reported yesterday.