Assessment rolls are public information. If you can't get the information online, you can consult the rolls at City Hall (first floor, just off the main foyer, to the left), or the Civic Centres in Etobicoke, North York, or Scarborough (City Clerk's department).
The assessment rolls are sometimes not up to date, especially if there has been a recent ownership change. For up to date information you can consult the Land Registry records (Atrium on Bay building, Dundas St. just west of Yonge, 4th floor). There is a charge, and you need a bit of experience finding your way around, but again these are public records.
If you can provide a street address, I could probably find the info from some "non-public" sources which I can access. Post the street address(es) here if you can.
