When the tenant does not pay the rent or only makes a partial payment, the notice you would serve is a Form N4 which gives the tenant fourteen days to pay or move out, this is under section 59 of the Residential Tenancies Act. If the tenant is persistently late in paying the rent you should serve the Form N4 each time the rent is not paid on the due date. Eventually after serving several of the N4’s then you would serve the tenant with a Form N8 which is the notice of termination based on persistent late payment of rent, section 58. If there is a fixed term tenancy agreement,  it can only be served at the end of the lease term and must coincide with last day of tenancy. You can obtain all the forms and more detailed information on the procedures from the Landlord and Tenant Board’s website at https://tribunalsontario.ca/ltb/forms/#landlord-forms.