Can sublease tenants claim tax return without a contract and consulting the landlord?
You do not need to worry about being sued. You may have to worry about being audited. This is serious enough that you need to hire a tax lawyer or accountant to advise you. They will not charge you much for a short consultation to obtain advise. That said, I would give a receipt to your sub-tenant for all rent paid that year. I would file an amendment to my tax return that I had filed, either changing the amount of the credit claimed for rent paid, and/or claiming the rent you received from the sub-tenant as income. This should be done before Revenue Canada contacts you.