Yup, Justin's correct about the way things are done in Ontario. Obviously, the landlord can deny tenancy from the onset without giving a reason (or, rather, it's easy for them to make up a reason to satisfy the Landlord/Tenant Act). However, I have had this problem in the past and have always come out on top.
I have rented where the lease says "no pets." I, of course, move in with all my reptile pets. Rarely do things escalate from there but one time my landlords were made aware of my apartments' contents through an illegal entry. Basically, the Landlord/Tenant Act in Ontario goes like this:
The landlord cannot evict the tenant based on the fact that he/she has pets (despite what it says on the lease). However, the landlord can evict the tenant if the pets meet any one or all of the following criteria: 1) The pets pose a danger to the general public (large constrictors, venomous animals, vicious canines, etc), 2) The pets are causing allergic reactions to another person in the dwelling, and/or 3) The pets are causing a disturbance to other tenants and/or the landlord (barking dogs, meowing cats etc).
Obviously, for most reptiles, it is impossible to apply any of these conditions and everyone's safe in Ontario.
Perhaps Alberta can follow suit....