[3][4][5] In her youth, she made the national team for taekwondo, where she is a black belt, before deciding to focus solely on soccer at age 12.

[22] After receiving offers to play for teams in the United States and Europe,[23] Lacasse signed with Icelandic club ÍBV in the Úrvalsdeild kvenna in 2015.

[41][42] She called the move a "dream", citing a desire to be part of a team with strong internal competition for playing time.

[43] On October 6, 2023, Lacasse came on as a substitute in an away match against Manchester United, scoring her first Arsenal goal in second-half stoppage time to help salvage a point in a 2–2 draw.

[44][45] Lacasse scored a goal in the 3–1 victory against Manchester United in front of the first sold-out crowd for a Super League match at Emirates Stadium.

In April 2021, Lacasse was called up to the Canada national team ahead of friendlies against England and Wales,[56][57] but did not appear in either match.

Given her minimal experience with the national team to that point, she later acknowledged "I knew it was ambitious" to hope to make the squad.

[60] Lacasse made her first appearance at a major international tournament as part of the national squad for the 2022 CONCACAF W Championship,[61] winning the silver medal, after a loss to the United States.

[63][64][65] Continuing to make appearances with the team into 2023, Lacasse was named to the Canadian roster for the 2023 FIFA Women's World Cup.

[68][69] In the second match, held on home soil at BMO Field, Lacasse scored in the first half to equalize a game that Canada would eventually win 2–1, clinching their fifth consecutive Olympic berth.