Air Canada said it has resolved computer-telecommunications issues that affected operations earlier today, but there will be delays and some cancellations due to the outage.
It is not yet clear what caused the outage. After around three hours, Air Canada issued an apology and said that things were on the mend.
The airline tweeted that it was "experiencing an interruption" at its contact centres and website and is working to restore service as soon as possible. "Thank you for your patience".
As Air Canada customers raised concerns about the situation, Toronto's Pearson International Airport also told customers over Twitter the airline was experiencing IT issues and that it was affecting flight schedules.
People hoping to fly on the airline are advised to check the status of their flights online.
The Air Canada AC8060 departure at 10 a.m. was cancelled and the airport is reporting that others may be facing delays.
A third and-as of 5 p.m. Monday-final tweet on the issue sent at 2:38 p.m. reported that "operations were returning to normal".