Emergency services, banking and retail were all affected by the outage of a major internet supplier.
Canada’s largest mobile and internet provider, Rogers, has apologised for the country-wide service outage which began on Friday.
The company’s CEO Tony Staffieri said the failure followed “a maintenance update in our core network”.
Transport, banking and emergency services were all hit by Friday’s blackout, with 911 hotlines and bank ATMs left unavailable.
Canadians flocked to coffee shops and libraries to find a connection.
The service outage began at 04:30 local time (08:30 GMT) on Friday and lasted for more than 15 hours, but most services have now been restored.
Mr Staffieri said the maintenance work “caused some of our routers to malfunction early Friday morning”.
The outage had a huge effect on a wide range of services across Canada, serving as a reminder of how reliant society has become on modern communications.
Many 911 services reported difficulties with incoming calls and hospitals asked on-call staff to come into work until the issue was resolved.
One mother, Lara Morgan, described how she struggled to contact emergency services after her son was injured in a rugby game with a suspected spinal injury.
Speaking to the Globe and Mail newspaper, she said she eventually found someone with a non-Rogers mobile phone to call 911, only to discover that ambulance services also relied on the Rogers network and were having difficulties dispatching paramedics. Her son eventually made it to hospital and was not badly injured.
In a statement, Mr Staffieri said the company was “particularly troubled that some customers could not reach emergency services”.
The outage also caused some events to be cancelled, including the Toronto tour date of Canadian singer The Weeknd. The gig was due to take place at the home of the Toronto Blue Jays, which is owned by Rogers Communications.
In Quebec province, a Montreal court had to delay a trial hearing for disgraced fashion mogul Peter Nygard after jail officials were unable to connect him to a videoconference system.
Critics say the outage demonstrated a need for more competition in the Canadian telecoms sector.
Three companies – Rogers, BCE Inc and Telus Corp – control 90% of the market share in Canada.
Rogers alone is the mobile carrier of nearly 11 million Canadians, with a stake in everything from hockey to cable television.