If the tenant has been paying rent persistently late throughout their tenancy, the N8 notice of termination can be served. Typically, you should be able to show the Landlord and Tenant Board that the tenant has been paying the rent late at least 7 or 8 times within a consecutive 12 month period.
To apply to the Board you will need to file the L2 Application along with a Certificate of Service. All the forms can be obtained from the Board’s website at https://tribunalsontario.ca/ltb/forms/.