On July 17, 2020, Houstan announced he would forgo his senior year, graduate from high school early, and reclassify to class of 2021.

As a sophomore, he averaged 10 points, 3.5 rebounds and 1.2 assists while shooting 53.1 percent on 3-pointers, helping lead the Eagles to a perfect 25–0 record, and ranked No.

[4] He was the only non-senior to start on a roster with talented players such as Scottie Barnes, Cade Cunningham, Moses Moody, Day'Ron Sharpe, and Zeb Jackson.

[7] Houstan was named to the 2021 McDonald's All-American Boys Game and Jordan Brand Classic rosters, becoming the first Michigan signee to earn the distinction since Daniel Horton in 2002.

[16] Houstan appeared as the first player off the bench in the season opener against the Detroit Pistons on October 19, but went scoreless with three rebounds and a blocked shot in 21:55.

[17][18] He made his first career start in place of the injured Mo Bamba on November 28 in a game against the Brooklyn Nets, and recorded seven rebounds in 30:52.

[21] Houstan was scheduled to represent Canada at the 2020 U17 World Cup and U18 FIBA Americas Championship, however, both events were postponed due to the COVID-19 pandemic.

[2][22] Houstan represented Canada at the 2021 FIBA Under-19 Basketball World Cup, where he averaged 17 points, 5.7 rebounds, 2.4 assists, and 2.3 steals per game, to help lead his team to a bronze medal.