If a regular person turns up to a realtor open house, they aren't turned away in Toronto. A contact is a contact, Ive been to a few as I was driving by, stopped in. As for checking if you are financially qualified, I supposed they can 'ask' but one is NEVER obligated to give out financial details.
They certainly do not ask for 'proof' before showing a home. Any open house is for the realtors to make new contacts, its not about selling one particular home.
When a home is for sale, there is often a feature sheet available to all, with floor plans and pertinent information.
Even for the 'appointment only' homes, one need only make an appointment to view the house.
I would not have an Open House if I were to list. Serious buyers could view the property or I might just give out my name, phone number etc to some builders working in the area. Pick a time and day when they can come over/call with offers and then, use a good real estate lawyer to do the fine print 'stuff'. In our area, the older homes are all being torn down for McMansions. My friend walked around the block and gave out eight cards with her number, took calls two nights later and saved all that commission.