Iga Swiatek outlasted Ukraine's Elina Svitolina 6-3, 1-6, 6-3 on Wednesday to book a Toronto title showdown with world number two Elena Rybakina.
Australian Open champion Rybakina delivered another gutsy comeback, beating fourth-seeded Coco Gauff 5-7, 6-2, 6-2 to reach Thursday's final in the hard court warm-up for the US Open.
Former world number one Swiatek, seeded seventh, is in her first final of the year, having last lifted a trophy in Seoul almost a year ago.
She improved to 5-3 against Svitolina, who had narrowed their head-to-head record with two wins over the Polish star this year.
In a match delayed more than an hour by rain, six-time major champion Swiatek raced to a 4-0 lead in the opening set.
The Ukrainian made Swiatek work to serve it out, saving a pair of set points in the final game of the first.
Energized, she raced through the second set before Swiatek rebounded in the third, breaking Svitolina to love for a 5-3 lead before holding serve to secure the win.
"Against Elina it's always tough, so I'm happy that I won this one," said Swiatek.
"Especially that I came back in the third set playing better. So, yeah, that's for sure a big improvement. I'm proud of myself."
Svitolina, who won the Canadian crown in 2017, was seeking her third 1000 level final of the season after winning at Rome and finishing runner-up in Dubai.
But she couldn't hang on as Swiatek upped her game again in the final set.
"Mostly I just wanted to adjust the quality," Swiatek said. "Because tactics can't do much if you're just not hitting the ball right. I knew I can do it, because I did it in the first set. I'm happy that I was patient enough to do that and didn't get disappointed or didn't give up."
Rybakina, who also rallied from a set down to beat Naomi Osaka in the quarter-finals, is on the cusp of her third title of the season after her triumph in Melbourne and a trophy in Stuttgart.
Her Canadian run has her inching closer to No. 1 Aryna Sabalenka in the rankings as the August 31 start of the US Open approaches.
TAKING OPPORTUNITIES
Kazakhstan's Rybakina polished off the victory over Gauff shortly before 1 a.m. local time, taking advantage as the American began to falter in the face of pressure on her serve.
"She served really well in the first set," Rybakina said. "It was pretty close the first one, and then I feel like on my serve I rushed a little bit in the end.
"I knew that I need to start straight away the second set well. I'm happy that I did a couple of good returns, and then things turned around."
While Rybakina had to battle past Osaka to reach the semis, Gauff had advanced via a walkover. But Rybakina said the hard work may have helped her.
"I guess the adrenaline and so many hours on the court helped a bit," she said. "In the third set also, few moments I felt like I was just swinging, and some crazy return at 30-all, and it went my way.
"So, I got my opportunities, I took them."