Travis Dodson, Josh Pauls and David Eustace also scored for the United States, which claimed a fifth championship title and ninth medal. Jack Wallace was a partner in three goals.
Billy Bridges was the only top scorer for Canada, which defeated the Americans 2-1 in the preliminary matches.
It was the replay of the 2019 final, which the United States won 3-2 in overtime. The 2020 tournament has been canceled due to the COVID-19 pandemic.
Earlier on Saturday, Russia crushed South Korea 7-0 to win the bronze medal.
The top five teams in the tournament qualified for the 2022 Beijing Paralympic Games. The Czech Republic beat Norway 2-1 on Friday to finish fifth.
Farmer opened the scoring at 7:28 in the first round in the power game. Dodson doubled the mark after a few minutes.
Bridges closed the lead 2-1 with less than a minute left in the first half.
Paul also took advantage of the power play in the second period to get the Americans back to top two. Farmer added a goal in the final moments of the clash.
Eustace sealed the match result in the last twenties.
Natalie Sinclair is a contributor at Vaughantoday.ca, covering a wide range of topics including local news, politics, business, technology, sports, entertainment, and lifestyle. She focuses on delivering clear, accurate reporting and useful information that helps readers stay informed about current events and issues that matter to their communities. Her work highlights timely developments, relevant stories, and practical insights in a professional and reader-friendly manner.