The self-assessment is done through the return of the business, essentially, and from time to time CRA audits those returns. They go on site or request information from the person and basically say, “You self-assessed this amount. Can you give us more information?” They have powers to request information from the business and essentially assess the situation of the business and see whether the self-assessment was conducted properly.
On November 6th, 2018. See this statement in context.