BCE Inc (BCE.TO), Canada's largest telecommunications company, said a hacker had accessed customer information containing about 1.9 million active email addresses and about 1,700 names and active phone numbers.
The breach was not connected to the recent global WannaCry malware attacks, the company said on Monday.
There is no indication that any financial, password or other sensitive personal information was accessed, said BCE, known as Bell to customers.
The company said it was working with the cyber crime unit and had informed the Office of the Privacy Commissioner.
The global WannaCry "ransomware" cyber attack infected 300,000 machines in 150 countries, making it one of the fastest-spreading online extortion campaigns in history.
(Reporting by Ahmed Farhatha in Bengaluru; Editing by Sriraj Kalluvila)