Serena kept her title defense on track rallying for a 4-6 7-5 7-5 win over Caroline Wozniacki while Venus booked her place in the final four by beating 14th seeded Spaniard Carla Suarez Navarro 4-6 6-2 6-3.
It will mark the 25th time the sisters have squared off and first since a 2013 semi-final clash in Charleston that Serena won.
While it is a matchup tennis fans always look forward to, for the sisters it is something they could live without.
“I definitely don’t like playing her,” explained Serena. “I think I’ve lost to her more than anyone on the tour. Definitely not a fun match.
“She’s tough. She has a great serve. She runs every ball down. She has a great backhand. She hits winners off the forehand.
“She does everything well, so it’s not an ideal matchup for anyone, to be honest.”
Despite the high praise, Serena holds a 14-10 advantage over her older sister in head-to-head meetings and has come out on top in their last five encounters, including the 2009 Wimbledon final.
But the sisterly clashes, which were at one time almost a regular and welcome occurrence on tennis courts across the globe, have become rarer-and-rarer.
In fact, Saturday’s meeting will be just the second in the last five years and Venus has a simple philosophy of how to play her sister.
“There’s no secret or science to it,” she said.
“I think that anyone who has gotten any wins against her, they’ve pretty much played the match of their life.
“Granted, I’d like to imagine that I hopefully won’t have to play the match of my life… but I know I need to play well.”
The other semi will pit third seed Agnieszka Radwanska against Ekaterina Makarova.
Poland’s Radwanska, the third seed, advanced with a dominant 6-2 6-2 win over Belarus’ Victoria Azarenka.
Unseeded Russian Makarova beat American qualifier Coco Vandeweghe 6-1 4-6 6-1.
Both Serena and Wozniacki arrived in Montreal in winning form.
Williams, a three-time champion on the Canadian hard courts, picked up her 61st career title last week at Stanford while Wozniacki was champion in Istanbul.
The match served up plenty of intrigue, Williams, the defending champion and current world number one, going against a former number one and former champion, who has her own love affair with the Montreal hard courts where she had built a 9-1 record.
The muscular American was certainly not going to outwork Wozniacki, who is training to run the New York City Marathon in November, but Williams had enough weapons and experience to see off the dangerous Dane.
At 34, Venus continues to prove she remains a force on the court out-lasting Navarro, who at 25 is nearly 10 years her junior.
“She (Venus) is been playing really well. She’s in really good form,” said Serena. “I definitely feel great when I see her playing so well.
“Obviously not when it’s time for me to play her but other than that it always is really good to see her playing really well.”-Reuters