Thank you for all of your replies.
Six months left on the lease and we are planning on getting a house somewhere outside of Toronto.
Here's some snippets from the letter received:
It poses a very concerning health threat to all of us and is causing headaches and itchy throats.
The smell is strong enough that it comes from the kitchen as far as our bedrooms and makes the kitchen unusable when the smell is present.
The smoke and toxic smell coming from the vents, fill out our unit every night and it becomes intolerable. We are extremely concerned about it as it can potentially be a health hazard.