The Canada Revenue Agency has the ability to ask financial institutions for data on all of their clients, if they wish. This is different than a warrant for just one of their clients. We refer to this as fishing, CRA is on the lookout for people who are making money and not reporting it on tax returns.
In the past CRA has asked eBay for listings of their clients and their clients activities. The same request was made a few months ago by CRA to PayPal. What CRA is doing is getting the data from PayPal and sorting by business. When they find a business with a large number of transactions, they will then use this listing to compare to their own records and see if these business have been reporting their income and their HST. This process has been described as the sharing economy meeting the underground economy. If you have been making transactions on PayPal and not reporting the income, then likely you will soon be hearing from CRA.