The first thing you should try is writing a letter to the tenants advising them that the smoke is bothering you and request that they smoke outside. If they do not comply you could then serve them with the legal notice (Form N5) that states that they are interfering with your reasonable enjoyment of the premises. When they are served with this notice they have seven days to correct the problem and if not corrected then you can file an application with the Landlord and Tenant Board to terminate the tenancy. It is uncertain that you would be successful in this case because the tenants could argue that their tenancy agreement did not include a non-smoking clause.