You can tell them you are not comfortable to give them SIN
Most of time, they will not insist. My land lord asked for SIN before and I refused, still got the place. However, it was in Halifax.
今天去Davisville 77 号看了一下房子，感觉不错，有室内的游泳池，楼层高，VIEW 不错，只是要等到12月才行，真矛盾！