Depends what your aim is here. If you are trying sell external home owner products like decking, pool accessories, or air conditioner installations (and you get a lead commission from companies), I would suggest that you might want to reach out to a middle of the road real estate agent and go into a venture with them. Depending where you are, there are some MLS real estate boards that allow their members to link to the internal database via an IDX (or similar word press plug in) and you can then list every listing you want from the MLS system in that area. If you are looking to gain advertising dollars via agents placing their listings with you for a fee and also having things like adsense, that's a bit of a different animal and an uphill battle because so many places already have nation wide contracts (eg point 2 point homes etc) to list all real estate listings on any/most MLS systems.
Also be aware that not all real estate overseeing boards allow this kind of joint venture of listing for sale homes if you're not a member of their association. They may view you as advertising or trading in real estate as a non licensed agent and wouldn't let you access to their listings once they found out what you are doing. Whereas:.... Others don't seem to worry so much about online ventures with non brokered advertisers (eg Kijiji). If you happen to find some semi retired agent who doesn't care too much about online website, other than getting the odd decent lead from it, you might find a good venture partner.
It's been ages since I played in the Real estate plug in/website area, so do some additional research. IDX is one of the data engines that allow you to hook up your website and active on call demand listings, I think there's DDX or something similar in some of the Canadian cities. It's a Hodge podge on how the boards allow the listings to be "fed" into a website. Good luck.