Probably out of contravention with zoning by-law for hardscape. You'd need to check the specific applicable by-law but from the generic mississauga one:
4.2.5.XX.3 Minimum landscaped soft area in the yard containing the driveway and walkway (%) 40% of the rear yard
Landscaped Soft Area means any outdoor area on a lot, located at grade, that is suitable for the growth and maintenance of grass, flowers, shrubs, trees and other vegetation, and including landscaping materials such as rocks and edging materials, but shall not include hard surfaced areas, such as driveways, aisles, parking areas, interlocking stone, and walkways. (0190-2014), (0212-2015)