I don't know Canada but where I am, you don't have a lease if you don't have the deposit. Like you said, if you haven't collected their check - and deposited it to know the funds were good - then you are at risk of them flaking out and leaving you with an empty rental, turning away other applicants in the meantime. That's not good business!
As a renter, I've never come across a landlord who would hold a unit for a signed contract without the money.
As a landlord, my lease says "The Premises will not be held for Occupant until owner receives this Agreement signed by Occupant and a check for the Payment Total listed on page 1. Subsequent monthly payments are due on the 1st of the month."
(Payment Total in this case is first month, last month, security deposit, pet deposit if applicable)
