The sister of Toronto Maple Leafs forward Phil Kessel moved in on a 2-on-1 and roofed a shot over goalie Shannon Szabados at 3:09 of the third.
Brianna Decker and Megan Bozek had the other goals for the U.S., which got two assists from Kendall Coyne.
Courtney Birchard and Caroline Ouellette scored for Canada. Marie-Philip Poulin added a pair of assists.
U.S. goalie Jessie Vetter made 14 saves for the win, while Szabados stopped 27 shots.
Canada, which beat the U.S. 3-2 in a shootout in round-robin play, defeated the Americans 5-4 in overtime in last year's final in Burlington, Vt.
The U.S. and Canada have met in every final since the tournament's inception in 1990. Canada holds a 10-5 lead in gold medals, but the U.S. has won five of the past seven tournaments.
Russia shut out Finland 2-0 to win the bronze medal earlier Tuesday.
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