I'm not a realtor/real estate agent, and I'm not the biggest fan of them, but I still believe that even buyers in the US who want accurate information will do best to work with an agent.

In the US, the availability of sale info. varies by region. Some states do not make sale prices public. And, Zillow and the like still exclude many areas of the US.

Although Zillow does often have accurate sale prices from either public records or from agents who listed properties on the site, it can't be trusted to be accurate. Even basic "factual" information (meaning things other than the made-up Zestimate) can be wildly inaccurate. Listing history for a given property is even less accurate, as not all properties are listed on Zillow and not all status changes (even things like "Under Contract") appear on Zillow. (That's just an aside... I don't think most people realize how inconsistent the information which makes it to Zillow is from region to region and even from agent to agent within a given region.)

And, without a realtor, even in states which make sale prices public on a public side to the local MLS, the NET sale price is not available. On the public side of my local MLS I can see gross sale price, but realtors can see the net sale price, which must be considered when figuring the real value of the property itself and using that info. to price another house. Buyers will roll closing costs and other things into the loan.

It looks like you should be able to cobble together some info. on sold prices in various areas of Canada in much the same way people do in the US.