Alcaraz, 21, swept to a 6-1, 6-1 victory over the Canadian in just 75 minutes and will meet Novak Djokovic in Sunday's final if the top-seeded Serb overcomes a knee injury and Italy's Lorenzo Musetti in the second semi-final.
"It has been an objective since the start of the year to try and win the gold medal and now we have one match left to try and get it done," said Alcaraz.
"I want to have fun in the final and do the business."
Spanish star Alcaraz, playing on the same Roland Garros court where he won the French Open in June, broke the 19th-ranked Auger-Aliassime three times in the first set, racing away with six consecutive games.
Alcaraz broke again in the fourth and sixth games of the second set on his way to claiming a fourth successive win over the Canadian having lost the first three of the pair's series.
"It was a very complete performance and I played at a very high level from start to finish," said Alcaraz.
"I had very good feelings and sensations, I'm so happy."
He added: "The final is very important for me and the Spanish people but I try not to think about how important it is and will focus on the match."
Wimbledon champion Alcaraz is the third Spanish man to reach the Olympic men's final after Jordi Arrese at Barcelona in 1992, Sergi Bruguera in Atlanta four years later and Rafael Nadal who won gold at Beijing in 2008.
He now has the chance to become the youngest men's champion since tennis returned to the Olympics at Seoul in 1988.
