Scott, a 16-year-old Calgary native, stopped 32 shots and was only beaten by Cayden Kraus's fluttering backhander in the first period.
"It's nice to get the win, it's all about results in this tournament and you just help the team by whatever means possible," said Scott. "I had lots of help. They had lots of power-play chances but our penalty killing shut them down and we had lots of power-play offence."
Alberta opened the scoring on the first power play of the game, 4:53 into the first period. Kyle Olson took the puck in deep and found the tape of Kobe Muir's stick in front and he fired in a high shot.
Manitoba got that one back a few minutes later when Kraus took the puck off the boards at the blue-line and let go a shot past Scott.
Manitoba owned the puck for much of the second period and forced Scott to make several tough saves to keep the game deadlocked at one apiece. Leif Mattson and Tyler Campbell each had great scoring chances denied while at the other end of the ice, Alberta's offence was stagnant— failing to register a shot until the period was almost half over.
But a couple of power plays late in the period gave the Albertans momentum and Manitoba eventually bent under the pressure.
Ethan McIndoe had his initial shot stopped but with very little net showing he put the rebound through the gap between the post and leg of goalie Dylan Myskew, who made 23 saves for Manitoba.
Alberta was nursing a one-goal lead eight minutes into the third period when the power play went to work again. Zane Franklin fanned on his one-timer from the point but the puck skipped over to Josh Patterson, whose snapshot from the face-off circle found the net to make it 3-1.
"We had to win that specialty teams battle, it's been big for us throughout the tournament and it will continue to be big for us," said Alberta head coach Michael Dyck. "We also knew we were going to need good goaltending and we'll need it on Sunday as well and Ian has provided it for us. He's been that guy all along."
Alberta went 3-for-5 on the power play, while Manitoba went scoreless on four chances with the man advantage.
"The penalties killed us, 5-on-5 we were up 1-0," said Manitoba captain Max Martin. "As a captain you lead your team through most games and at the end of a loss you feel you haven't done your job, but we still get to play for a medal and it's not the end of the world here."
Alberta will play for gold Sunday against Ontario, which beat Quebec 5-2 in the other semifinal. Manitoba and Quebec will face each other for bronze.