In Ontario, Canada: do you have to provide your landlord your date of birth; Employer's Phone number; next of Kin's name and phone number?

It's fairly common practice to want to assess a person's creditworthiness, and asking for employer information and date of birth would be useful and arguably legitimate to that end, but for existing tenants? Nah, there's no obligation to comply with such requests, generally speaking (though there might be exceptions for subsidized housing and other special programs).

Once you're in a rental property, in Ontario, you typically have 'security of tenure', and there are finite reasons that they could evict you - non-payment of rent, habitual late payment of rent, damage to the property, interfering with the reasonable enjoyment of other tenants, illegal actions in the rental unit, landlord needs the unit for personal or family use, landlord is converting the property to non-residential purposes, etc.

All that being said, I'm not generally a big fan of fighting with your landlord unnecessarily. I think the question you've posed here - WHY - is a good question in context, and I'd put it to the landlord if I were you. If they say that they want it to assess your creditworthiness, I'd answer that they can look at my records of having paid my rent on time for nine years. (Actually, *I* might follow up by pointing out to them that even if I were unemployed with awful credit, they'd have no basis to act on that unless I stopped paying my rent. But you have to be delicate when 'lawyering' a landlord.) Or they might say they're just trying to complete the information in their file, in which case the response is, again, "Yes, but why do you need that information in the first place? What do you plan to do with it?" Front line workers in a property management company will be totally unequipped to deal with that question, but PIPEDA requires organizations (including residential landlords in Ontario) to be reasonable in terms of their collection of personal information, and gives individuals the right to know (and consent) to the reasons and uses for the personal information being collected.

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I know in America some of the information is necessary to verify if you're a decent person. Like no one wants a tenant that's a jerk. I don't know why they would need your birthday unless they plan on giving you a present when it comes around (which frankly would be pretty awesome). As far as legality is concerned I don't know. It seems like the sort information you should to be allowed to withhold. Best thing to do is talk with an actual expert (as I am merely a person giving an opinion) and see if they know what you should do. If you really just don't want to give out that information then you should keep looking for a new place to rent. If it turns out other places ask for it too then you can assume that it's legal information that these places need (however be very cautious about believing assumptions as they might not always be accurate that's why asking a true expert would be the best thing for you to do).

Maybe they want to bake you a cake.

No, you're not required by law to give them that information. Neither are they required by law to rent to you.

No you are not. Also, they are not required by law to rent to you. Your call.