Canada trailed 2-0 before Brianne Jenner and Poulin scored in the final 3:26 of regulation, and Poulin had the game-winner with a power play goal at 8:10 of overtime.
Shannon Szabados made 27 saves for Canada, which has won 20 straight in the Winter Games since the Nagano final in 1998. That was the only gold medal for the United States, which has lost in the Olympic final to Canada three times since then.
Jesse Vetter made 28 saves for the Americans. Meghan Duggan and Alex Carpenter scored for the U.S.
Switzerland beat Sweden for the bronze medal.