In recent years, CRA has particularly focused on tracking underground economy activities. One way they are doing this is by obtaining information from key 3rd parties.
For example, recently CRA obtained details from contractor credit applications submitted to Rona. Consider the type of information that Rona would have: name, address, and other specifics that would help determine whether credit should be given. Presumably CRA could compare information reported on a credit application to the contractors’ tax returns.
CRA has also recently obtained information from Square Canada. Many smaller vendors accept payment by swiping the customer's credit card through a little square plastic device connected to the audio jack of a phone or IPad. Square Canada provides this payment processing device, a Square Reader. Through a Federal Court Order issued to Square Canada, CRA obtained identifying vendor information and sale details associated with individuals or entities using these devices. The information request primarily focused on those with annual revenues of $20,000 or greater, for the 2012-2015 and part of the 2016 year.
It would not be unreasonable to expect that CRA could obtain similar information from other websites, web-based apps and organizations.