Fisher was born in Oshawa, Ontario, the second of five children of Thelia and Rohan Fisher.[1] At age 12, as a seventh-grader, he competed for the under-18 high school team at Crestwood Preparatory College in Toronto.[2] Fisher became the first middle school student to play for Crestwood Prep's varsity team.[3] By the age of 13, he stood 6 ft 5 in (1.96 m).[4] He was considered by many analysts to be the number one player in his class as he entered high school.[5][6][7]
Fisher was a consensus five-star recruit and one of the top players in the 2023 class; before reclassifying to the class of 2022.[8][9]
Fisher represented Canada at the 2021 FIBA Under-19 Basketball World Cup in Latvia.[11] In his national team debut on July 3, he scored 11 points in an 80–71 win over Lithuania.[12] Fisher averaged 6.9 points and 3.4 rebounds per game, helping Canada win the bronze medal.[13]