No, a tenant cannot be evicted simply for having a roommate. However, a tenant may be evicted if the roommate is causing a problem for the landlord or for other tenants. For example, if the roommate is making a lot of noise, damaging the unit, or there are too many roommates (overcrowding), the landlord can serve a notice of termination and apply to evict the tenant and any other occupants of the unit.

Source: www.sjto.gov.on.ca