Front Street between Church and Jarvis could make for a superb pedestrian space. I'd configure it as a market square-type space where restaurants could have massive patios onto the square, and where all sorts of outdoor markets, concerts, and events could take place. It would be cobblestoned with fountains and greenery.
A square at this location would likely be a more pleasant and attractive public space than Nathan Phillips Square or Dundas Square on account of the heritage atmosphere, the diversity of businesses fronting directly onto the square, the market buildings, and the lack of massive billboards.The views of the downtown skyline are iconic, too, with the Gooderham Building and the skyscrapers behind it.