[3] Buchanan spent two years playing college soccer at Syracuse University between 2017 and 2018, making 33 appearances, scoring 12 goals and tallying six assists.

[6] After two years with the Orange, Buchanan left early and signed a Generation Adidas contract with Major League Soccer ahead of the 2019 MLS SuperDraft.

[13][14] The $7 million transfer fee (with a 10% sell-on clause) paid by Club Brugge was a club-record received by the Revolution for one of their players.

[23] Buchanan was named to the Canadian U-23 provisional roster for the 2020 CONCACAF Men's Olympic Qualifying Championship on February 26, 2020.

[31] He scored his first goal for the senior team on July 29 against Mexico in the semi-final stage of the Gold Cup, netting the equalizer in an eventual 2–1 defeat.

[32] Buchanan's play at the tournament was widely praised by the region's media and at the conclusion of the competition he was named as the recipient of the 2021 CONCACAF Gold Cup Best Young Player Award.

[34] In Canada's second match on November 27 against Croatia, the team scored their first ever goal at a men's World Cup, with Buchanan sending in a cross that was met by the head of Alphonso Davies and sent into the back of the net.

[37] After Canada advanced to the knockout phase, Buchanan would suffer a broken tibia while training for the quarterfinal match against Venezuela, and would undergo surgery to repair the fracture.