Thomas, who had played 3:58 through the first two periods of the game, tipped a long pass by Calen Addison (Pittsburgh Penguins) through Russia defenseman Daniil Misyul (New Jersey Devils) and deep into the offensive zone. He won the race to the puck, pulled it around Russia goalie Amir Miftakhov and tucked it inside the post.
Connor McMichael (Washington Capitals) had a goal and an assist for Canada, which won the World Junior Championship for the first time since 2018, and for the first time outside North America since the 2008 WJC in Czech Republic.
Dylan Cozens (Buffalo Sabres) and Barrett Hayton (Arizona Coyotes) scored for Canada, and Addison (Pittsburgh Penguins) had three assists. Joel Hofer (St. Louis Blues) made 35 saves.
Grigori Denisenko (Florida Panthers) had a goal and an assist for Russia, and Nikita Alexandrov (St. Louis Blues) and Maxim Sorkin (2020 Draft eligible) scored. Miftakhov made 26 saves.
Russia took a 3-1 lead on Sorkin's goal at 8:46 of the third period, but McMichael scored 34 seconds later when a shot by Addison (Pittsburgh Penguins) deflected off both his skates and past Miftakhov.
Hayton, who was a game-time decision because of a left shoulder injury sustained against Finland in the semifinals Saturday, tied the game 3-3 with a power-play goal at 11:21.
Sweden 3, Finland 2 -- Linus Oberg, a forward prospect for the 2020 NHL Draft, scored the go-ahead goal at 13:19 of the second period and Sweden held on to win the WJC consolation game.
Oberg was first on the puck after a shot by Linus Nassen (2020 Draft eligible), and his shot from below the goal line from a sharp angle went off the left skate of Finland goalie Justus Annunen (Colorado Avalanche) and in the net.
Samuel Fagemo (Los Angeles Kings) scored his tournament-best eighth goal and Rasmus Sandin (Toronto Maple Leafs) scored on the power play. Hugo Alnefelt (Tampa Bay Lightning) made 32 saves.
Sweden finishes third after a sixth-place finish at the 2019 WJC. It lost 2-0 to Switzerland in the quarterfinals.
Patrik Puistola (Carolina Hurricanes) and Matias Maccelli (Arizona Coyotes) scored for Finland and Annunen made 23 saves. Finland, the 2019 WJC winner, finishes fourth.
Things we learned
Hayton played through pain
Barrett Hayton (Arizona Coyotes) played through significant pain in his left shoulder to score the game-tying goal and help Canada win the WJC championship Sunday.
Hayton was injured when he fell into the boards early in the third period of the semifinals against Finland on Saturday and was a game-time decision Sunday.
"Obviously I didn't want to miss this game for anything," Hayton said. "But that being said, I didn't really know [if he'd play]. The medical staff did an unbelievable job. I owe to them for giving me this opportunity.
"Definitely some pain, but when you're out there, in that atmosphere, you don't really feel much. You just play. When you're in that moment you don't feel those injuries."
He certainly wasn't feeling much pain when he snapped a shot from the right face-off circle at 11:21 of the third period to tie the game 3-3.
"I definitely felt it a little bit but I put my all into that shot," Hayton said.
Hayton was Canada's captain and leading scorer with 12 points (six goals, six assists), and on Sunday also was an inspiration.
"That's why he's our captain," coach Dale Hunter said. "He wanted to play. And to zip that puck, you know, that was a heck of a shot. For him to show up and do something like that is special. He led the way."
Lafreniere named MVP
Alexis Lafreniere, expected to be the No. 1 pick of the 2020 NHL Draft, was named the most valuable player and best forward at the WJC.
The 18-year-old Canada forward had two assists in the championship game against Russia and 10 points (four goals, six assists) in five tournament games. He missed the final two games of the preliminary round because of an injury to his left knee.
Lafreniere's teammate Joel Hofer (St. Louis Blues) was named the best goaltender. After replacing Nicholas Daws (2020 Draft eligible) during the second period against Russia on Dec. 28, Hofer allowed nine goals on 148 shots (.939 save percentage) in six games.
Rasmus Sandin (Toronto Maple Leafs) was named the best defenseman. He led the position and was tied for fourth among all skaters with 10 points (three goals, seven assists) in seven games.
Lafreniere, Hofer and Sandin also made the Media All-Star team, along with Canada forward Barrett Hayton (Arizona Coyotes), Sweden forward Samuel Fagemo (Los Angeles Kings) and Russia defenseman Alexander Romanov.
Fagemo led all players with eight goals and 13 points. Hayton was second in scoring with 12 points (six goals, six assists).
United States forward John Beecher (Boston Bruins) was given a one-game suspension Sunday for boarding Finland forward Eemil Erholtz (2020 Draft eligible) during the first period of a 5-0 loss in the quarterfinals Thursday.
If Beecher plays for the United States at the 2021 WJC, he will be suspended for the first game.
Groups set for 2021 WJC
Canada will play its preliminary-round games at Rogers Place, home of the Edmonton Oilers, at the 2021 World Juniors.
The 2020 WJC champion will be in Group A, along with Finland, Switzerland, Slovakia and Germany.
The United States will be in Group B, along with Russia, Sweden, the Czech Republic and Austria, and will play its preliminary-round games at ENMAX Centrium in Red Deer, Alberta.
Germany to return in 2021
Dominik Bokk (Carolina Hurricanes) scored two goals to help Germany to a 6-0 win against Kazakhstan in the final game of the best-of-3 relegation round.
The victory means Germany will play in the 2021 WJC in Edmonton and Red Deer, Alberta, while Kazakhstan will play one level down, in the WJC Division IA.
"It was just important to give the opportunity to guys to come next year to play in the top division," said Germany captain Moritz Seider (Detroit Red Wings), who had an assist Sunday and six assists in seven games. "Everybody was focused, everybody was dialed in today and I think we deserved the win."
Austria, which won the WJC Division IA tournament in Belarus last month, will replace Kazakhstan for the 2021 WJC.