I find the resistance to having sold information more readily available to be rather interesting, for the reason that I actually don't think it will affect the real estate market itself in Toronto or Vancouver a whole lot at all. I recognize that it would affect realtors as a profession, pushing them to have to focus more on service as opposed to mere data providing.
In the heated areas of Toronto, public sold data will reveal to prospective buyers just how much these homes are really selling for. Too often, potential buyers peruse previously sold house listings and see the asking price (which is obviously under market value) and then actually think that they can afford the next one in that neighborhood. If only buyers knew what properties are truly selling for, there will be fewer stories of disbelief when houses sell for "120% over asking!" when in reality, they're just selling for market value.
Conversely, for sellers, it'd also help them realize what other houses in their area are going for and what potential buyers are willing to pay for them. Since most go for over asking, it may actually raise their expectations when it comes to offers.
Both of these factors, IMO, will come into play and at the end of the day, I don't know that much will change as far as cooling the hot market. Buyers aren't going to be, all of a sudden, buying houses at under market value...and sellers aren't, all of a sudden, going to be selling at below market value. Having historical sold data is an invaluable tool for both buyer and seller so let's just let it be available.