No.12 seed Angelique Kerber leads her head-to-head against former World No.10 Daria Kasatkina 4-3. The three-time Grand Slam champion won their only previous Canadian encounter 6-2, 6-2 in the 2016 Montréal quarterfinals, as well as their 2017 Tokyo second-rounder and their two most recent meetings, at Eastbourne and Wimbledon last year. Kasatkina's victories have come at Sydney and Doha in 2017, and at Indian Wells in 2018.
No.15 seed and 2010 champion Caroline Wozniacki is all square at 1-1 against Yulia Putintseva, having been upset by the Kazakh 1-6, 7-6(3), 6-4 in the first round of the 2016 Australian Open but gained a 6-0, 7-5 revenge in the second round of Sydney one year later.
No.13 seed Johanna Konta faces a rematch of her Eastbourne opener in June against rising 19-year-old Dayana Yastremska. The Briton won that match - their only prior encounter - 6-2, 6-4.
Two former junior World No.1s clash for the first time as No.11 seed and 2015 champion Belinda Bencic, the 2013 Wimbledon girls' titlist, takes on 2016 Wimbledon junior winner Anastasia Potapova. The 18-year-old Potapova will be bidding for her third Top 20 scalp of the year following defeats of Anastasija Sevastova in Prague and Angelique Kerber at Roland Garros.
Aliaksandra Sasnovich comes into Toronto bidding to snap a seven-match losing streak dating back to Madrid. The Belarusian is 2-0 against Elise Mertens, having triumphed 2-6, 7-5, 6-2 in Cincinnati qualifying in 2017 and 7-6(5), 7-6(3) in the first round of Wuhan last year.
No.16 seed Anett Kontaveit lost her only previous meeting with wildcard Maria Sharapova 6-3, 6-4 in the 2017 Stuttgart quarterfinals - the Russian's first tournament back following her 15-month suspension, and Kontaveit's first run to the last eight of a Premier tournament.
Julia Goerges is 4-2 against Polona Hercog in a rivalry stretching back to 2010, including 2-0 on outdoor hard courts: a 6-3, 7-6(3) win in the first round of the 2012 Australian Open and a 6-4, 6-4 win in the 2018 Auckland quarterfinals, their most recent meeting. Hercog's only victories in the series have come on clay - in Fed Cup play in 2011 and in Bastad in 2012.
Kristina Mladenovic and qualifier Jennifer Brady's only previous encounter was a dramatic 3-6, 6-3, 9-7 win over two hours and 59 minutes for the Frenchwoman in the first round of Roland Garros 2017. Mladenovic would go on to reach her second Grand Slam quarterfinal at that tournament.
ORDER OF PLAY (all courts except Court 4 start 11am)
Dayana YASTREMSKA (UKR) vs  Johanna KONTA (GBR)
[WC] Leylah FERNANDEZ (CAN) vs [Q] Marie BOUZKOVA (CZE)
 Caroline WOZNIACKI (DEN) vs Yulia PUTINTSEVA (KAZ)
Not before 7pm
[WC] Maria SHARAPOVA (RUS) vs  Anett KONTAVEIT (EST)
 Angelique KERBER (GER) vs Daria KASATKINA (RUS)
[Q] Jennifer BRADY (USA) vs [WC] Kristina MLADENOVIC (FRA)
 Belinda BENCIC (SUI) vs [Q] Anastasia POTAPOVA (RUS)
[Q] Polona HERCOG (SLO) vs Julia GOERGES (GER)
Not before 5pm
Caroline GARCIA (FRA) vs Jelena OSTAPENKO (LAT)
[WC] Svetlana KUZNETSOVA (RUS) vs [Q] WANG Xiyu (CHN)
Elise MERTENS (BEL) vs Aliaksandra SASNOVICH (BLR)
Sofia KENIN (USA) vs HSIEH Su-Wei (TPE)
[WC] Eugenie BOUCHARD (CAN) / Sharon FICHMAN (CAN) vs Nadiia KICHENOK (UKR) / Abigail SPEARS (USA)
Petra MARTIC (CRO) vs [Q] Francesca DI LORENZO (USA)
COURT 4 (starts 12 noon)
Monique ADAMCZAK (AUS) / Storm SANDERS (AUS) vs  Victoria AZARENKA (BLR) / Ashleigh BARTY (AUS)
Miyu KATO (JPN) / Sabrina SANTAMARIA (USA) vs [WC] Françoise ABANDA (CAN) / Carson BRANSTINE (CAN)