My understanding is that landlords are free to regulate smoking in the public areas of their building, such as the lobby, and laundry room, etc.
There is also a City of Toronto bylaw that forbids smoking within 9 meters of any entrance to the building:
https://www.toronto.ca/community-people/health-wellness-care/health-inspections-monitoring/smoking-legislation-enforcement/municipal-smoking-bylaws/mc-chapter-709-smoking/To ban smoking in individual units requires them to have made that stipulation in your lease, otherwise they can't.
However, they do have a duty to enforce the "reasonable enjoyment of the premisses" provisions within the RTA. So if you smoke, and if that smoking interferes with the reasonable enjoyment of your neighbours (smoke getting into other apartments through the ventilation system?), or if the smoking presents a health concern for their employees (second hand smoke getting into the hallways?), then they might have grounds to file a complaint at the LTB.
In practical terms, what I believe this all means is that you can continue to smoke in your unit. If someone complains to your landlord, then they would have to warn you before it would be reasonable to file a complaint at the LTB – so in other words, you will receive a warning if your smoking bothers your neighbours. If your smoking is a problem, then you could look into getting an air-filter, or exhaling your smoke out an open window, etc., to mitigate the complaints.
Also (and I don't know whether this applies to your situation), you have a right to take whatever medical treatments you require, so if you happen to be smoking medical marijuana, then they can't really do anything to stop you.