Canada started it's first experimental reactor in 1945, before the UN even existed. In 1954 work started on an electric generating plant, which was brought online in 1962. In 1965 a second generating station was in operation, with more completed by 1973. Sales of reactors to foreign countries started in 1974 to Argentina, with more sold later to China, South Korea, India, Pakistan and Romania. There was no monitoring by foreign agencies when it first started, but there were treaties (I think) with the USA promising not to develop nuclear weapons. Obviously the Soviets didn't make any similar promises, neither did USA. Out of 232 nuclear reactors in the world today, 27 are Canadian-designed and built CANDU reactors, with 10 reactors operating in foreign countries. And we still don't have any nuclear weapons (officially).

Canadian nuclear history

Canadian nuclear faq

Nuclear tech in Canada has had some difficulty since the late-90s, with four units always offline, and no money to maintain them. After the 2003 blackout, all 11 operational reactors in Ontario disconnected from the grid, and only 4 were able to step back up within several hours. The Ontario government also sold a few units to British Energy as part of a privatization agenda.