There is no "several years" requirement.

In Vancouver, flipping has become some people's main and often only income source yet it's not taxed as such, in part because CRA auditors are chasing people for nominal adjustments or because until 2016 one didn't even have to report the sale of their home on their tax return. 

People move into a fixer-upper, live there with their kids while renovating a home they never intended to live in for the long-term, or they buy a home, tear it down and rebuild while renting, and then sell for a tax free "principal residence" gain.  They pay zero income tax, even though they've done this repeatedly for the past 10 - 15 years and the CRA has no resources, paper trail, or the will to investigate further.

These people consider themselves smart or entrepreneurial, but if you consider that they pay less income tax than your maid who works 2-3 jobs, then I consider them leaches benefiting from incompetent government.