Most listings are in the $20's per square foot per year. The Toronto region is experiencing a a boost in rates. In the last 3 months, the median rate increased $28 per sqft per year.
In the last 90 days, 10 listings have been posted online, which means office spaces are probably going fast. You'll want to be prepared to make an offer immediately. About 10% of the office spaces in the Toronto are subleases, so you will probably have to consider a longer term lease. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,620 sqft. Most properties in this region are around 8 floors. Most buildings in this area were built in 1980 and are Class A.