She was up 3-1 in the first set when American opponent Serena Williams called for a medical timeout.
Microphones picked up Williams referencing back spasms when she spoke to Andreescu.
Andreescu became the first Canadian to win the Rogers Cup women's singles title in 50 years.
With these points, Bianca will make a debut in the top-15 on Monday and we should see a lot from this outstanding teenager at the US Open, heading to NY as one of the favorites if she brings her 'A-game'. She'll wake up tomorrow ranked 14th, the highest-ranked teenager on Earth.
Andreescu is returning from a right shoulder injury that sidelined her since the French Open in May.
"Within my lifetime there hasn't been that many - I'm 34 and there hasn't been many Canadians up there in the top rankings", says recreational tennis player Luke Naka.
Clearly doing better physically, Andreescu screamed as she tied the third set 3-3, but Pliskova fired two aces for the final two points of the seventh game to retake the lead.
After the chair umpire announced Williams's retirement the former world No. 1 started to cry on her bench.
There was the rising Canadian tennis star, 19-years-old, entering Centre Court at the Aviva Centre preparing to play in the biggest match of her life against one of the best-ever tennis players in Serena Williams.
Canadians Faye Urban and Vicki Berner played in the 1969 final, with Urban winning the tournament that was played on clay and called the Canadian Open. "I tried but I just couldn't do it", a tearful Williams, who struggled to get the words out, told the crowd. "I know what it's like to pull out of tournaments and be injured". "But I just I couldn't do it. Thanks to Jehovah for letting me come out here". "I kept telling myself 'never give up.' I'm trying to look at my injury not as a setback but more of a challenge".
"I'm sorry I couldn't do it today".
She will face either three-time Rogers Cup champion Serena Williams or qualifier Marie Bouzkova on Sunday, with a chance to lay claim to her second career WTA Tour-level title.
"Bianca, you're a great sportswoman".
Williams entered the match looking for a fourth Rogers Cup title.
She'll play the victor of the second semifinal between American Serena Williams and Marie Bouzkova of the Czech Republic. Sixteenth-seeded Gael Monfils then withdrew before his semifinal against world No. 1 Rafael Nadal. On the men's side, Milos Raonic retired after two sets against Felix Auger-Aliassime in a much-anticipated all-Canadian matchup.
"I try to channel that pressure into something good", said Andreescu.