CRA can issue an income tax or GST/HST assessment even if a tax return has not been filed. This is called an arbitrary assessment and CRA can then proceed to collect the tax debt assessed even if the amount is wrong.
Disclaimer:
"This article provides information of a general nature only. It is only current at the posting date. It is not updated and it may no longer be current. It does not provide legal advice nor can it or should it be relied upon. All tax situations are specific to their facts and will differ from the situations in the articles. If you have specific legal questions you should consult a lawyer."