The Russian right-hander's withdrawal was reported on the competition's Twitter channel, which included that Romania's Simona Halep had now been lifted to second seed.
World number one Serena Williams will be pursuing her fourth Rogers Glass crown after wins in 2013, 2011 and 2001.
Five-time Stupendous Hammer competition champ Sharapova, beaten by Williams in the current year's Australian Open last and the Wimbledon semi-finals, has never won the Rogers Glass.
The hardcourt competition is one of a few tune-up occasions driving into the US Open, where Williams will be endeavoring to finish a datebook year scope of every one of the four tennis Thousand Hammer occasions. (AFP)