Short answers, pulled from the story.
Igor Gouzenko, a Soviet cipher clerk at the Soviet Embassy in Ottawa, defected in February 1946 and provided Canadian officials with documents exposing an active Soviet spy ring inside the country. Historians have marked the Gouzenko Affair as the moment that launched the Cold War era for Canada, triggering a red scare and shaping the country's subsequent security policies.
Lester B. Pearson introduced the United Nations Emergency Force during the Suez Crisis of 1956, establishing the first peacekeeping force in UN history. The underlying concept had originally been proposed by Prime Minister Mackenzie King and Secretary of State Louis St. Laurent at the United Nations Conference in San Francisco in June 1945, but was not adopted at that time.
Prime Minister John Diefenbaker refused to place Canada's military on immediate war alert as the United States demanded, calling instead for United Nations intervention. Only after a direct phone call from President Kennedy did Canada's armed forces begin preparing for "immediate enemy attack." The episode deepened the governing party's disarray over the nuclear question and contributed to Diefenbaker's loss in the 1963 election.
Alexander Yakovlev served as Soviet Ambassador to Canada from the mid-1970s for a decade, during which he and Prime Minister Pierre Trudeau became close friends. In the early 1980s, Yakovlev accompanied Mikhail Gorbachev on a tour of Canadian farms, and the two men began discussing the need for liberalization within the Soviet Union. Yakovlev later returned to Moscow and was called the "godfather of glasnost," the intellectual force behind Gorbachev's reform program.
Project Spinnaker was a secret joint Canada-United States program launched in response to Canada's 1987 White Paper on Defence, designed to deploy acoustic listening posts on the Arctic seafloor to monitor Soviet submarine traffic. It required a large autonomous underwater vehicle named Theseus, capable of operating in permanently ice-covered waters. In the spring of 1996, Theseus was deployed from CFS Alert on Ellesmere Island and laid 180 kilometres of fibre optic cable on the seafloor, reaching an acoustic array at the edge of the Continental Shelf.
Canadian forces withdrew from NATO commitments in Germany, military spending was cut, and the Diefenbunkers fallout shelters were decommissioned. In 1994, the last active American military base on Canadian soil, Naval Station Argentia in Newfoundland, was decommissioned and transferred to the Canadian government; the station had stored the Mk 101 Lulu and B57 nuclear bombs and served as a key node in the US Navy's SOSUS submarine detection network.