McCabe put his team ahead with a pair of identical goals, scoring through goalmouth scrambles in the first period.
"It feels awesome, especially in such an emotional game against Canada," McCabe said. "I'm so proud of my team. This was the best game of the tournament for us."
In the final, the Americans will face defending champion Sweden. The Swedes beat Russia 3-2 in a penalty shootout, with Sebastian Collberg scoring the winner.
Gaudreau made it 3-0 for the Americans, beating Malcolm Subban with a low shot on a sharp counter attack at 22:58. Subban was substituted for Jordan Binnington after stopping 12 of 16 shots, and Jim Vesey extended the lead to four 10 minutes later.
Ty Rattie scored one for Canada with a short-handed goal at 44:03, but Gaudreau scored on another sharp attack with 4:19 to play.
United States goalie John Gibson made 33 saves for the victory.
"The defense played really well, which made my job a lot easier," said Gibson, who made three tough saves when his team was a man down after Rattie's goal. "If it wasn't for them, we probably wouldn't be here."
The Americans finished third in their group at 2-2 in the preliminary round and routed the Czech Republic 7-0 in the quarterfinals on Wednesday.
Canada didn't lose a game in the preliminary round and had a quarterfinal bye.
Elias Lindholm and Filip Forsberg scored in the late game as Sweden dominated the first period, but Russia pulled one goal back midway through the second period and Mikhail Grigorenko tied it at 47:56.
Neither team scored in overtime before Collberg turned out to be the lone scorer in the penalty shootout.
Niklas Lundstrom made 27 saves for the victory. Andrei Vasilevski stopped 38 shots for Russia.
Slovakia beat Latvia 5-3 in a relegation-round match.
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