“The key issue here isn't whether or not you sign a lease, but whether your mother, as the landlord, is acting in "good faith" under Section 48 of the RTA, which allows a landlord to terminate a tenancy if the landlord or a specified family member (which includes a child of the landlord) requires the unit for their own use for at least one year. If your mother ends the tenancy so that you can move in, but then it turns out that you're not actually living there as your primary residence, this could be seen as acting in bad faith.

That said, if you move into the unit and use it as your primary residence, and then decide to sublet part of the unit (with your mother's consent), this could still be within the rules, as long as you're genuinely living there.”