Ranked 132nd in the world, 22-year-old Anisimova beat eighth-seed Emma Navarro 6-3 2-6 6-2 an all-American semi-final in Toronto on Sunday.
The former world No.21 will face third-seeded defending champion Jessica Pegula in the decider. Fellow American Pegula defeated Diana Shnaider of Russia 6-4 6-3 in the other semi.
Anisimova took her eight-month break from tennis last year, saying she had been struggling with her mental health and burnout. She has two WTA Tour titles - in 2019 in Bogota and 2022 in Melbourne.
"I didn't want to finish my career on that note," she said. "I had sacrificed so much and given so much to the sport."
At age 17, Anisimova reached the 2019 French Open semi-finals after beating reigning champion Simona Halep - the youngest woman to get that far at a major since 2006.
She has three times reached the fourth round of the Australian Open, beating defending champion Naomi Osaka at the 2022 event in Melbourne and only falling to eventual champion Aryna Sabalenka earlier this year.
This week she has beaten four top-20 players to reach the final - No.3 Sabalenka, No.12 Daria Kasatakina, No.15 Navarro and No.17 Anna Kalinskaya.
Saturday's win over second-seeded Sabalenka - 6-2 6-2 - in the quarter-finals was her first victory over a top-10 player in nearly two years.
"I was trying to fight," Anisimova said. "I'm just happy with how I was able to pull through."
- with AAP
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