Sharapova beat Germany's Tatjana Maria 6-1, 6-4 while Raonic was beaten 6-7 (5/7), 7-5, 6-4, 7-6 (7/4) by Lucas Lacko.
Hobart International: Defending champion Elise Mertens reaches quarters; Irina-Camelia Begu crashes out
Elise Mertens is the only seeded player left in her half of the draw and one of just three remaining in the tournament.
Auckland Classic: Caroline Wozniacki cruises into second round, defending champion Lauren Davis crashes out
There were no problems for Wozniacki after the Dane recovered from a rough start to romp home 6-3, 6-0 against American Madison Brengle.
Maria Sharapova made a triumphant return to Grand Slam competition after a 15-month doping ban, outlasting second-ranked Simona Halep 6-4, 4-6, 6-3 at the US Open on Monday.
US Open 2017: Garbine Muguruza kicks off campaign with easy win over Varvara Lepchenko, Petra Kvitova advances
Despite winning two Grand Slam titles, Muguruza has never felt at home at Flushing Meadows as she has never advanced past the third round in US Open.
Canadian Open: Jelena Ostapenko, Kristina Mladenovic suffer first round upsets, Petra Kvitova advances
It was another disappointing Canadian outing for Mladenovic, who has never won a match in Montreal or Toronto.