Guarantor is just a reference, for the applicant's credit, personal character. You do not need to bear financial responsibility for your friend who is the tenant renting that apartment. The tenancy act in Ontario protects tenants in certain way, but it can not stop the landlord from evicting the tenant if the rent can not be paid in full or in time. Your friend must have paid rent deposit prior to moving in that apartment. What could happen(in my personal opinion) could be, the deposit he paid would not be credited back and his name would be flagged by that rental company since then. It all depends on what terms and conditions of the lease, but you probably don't need to worry too much.