Hmmm really? Just off the top of my head...
CN Tower
Ripley's Aquarium
Roundhouse Park/Train Museum
Hockey Hall of Fame
Tourists usually see all these places no matter what, as they are the "must-visits" and right next to each other. The synergy is great between them, and probably a big part of why Ripley's is as successful as it is.
ROM
AGO
Centre Island/Waterfront
Casa Loma
Bata Show Museum
Kensington Market
St. Lawrence Market
For sure!
Fort York
Science Centre
Toronto Zoo
Aga Khan Museum
Black Creek Pioneer Village
Scarborough Bluffs
Fort York is kinda boring, and not really something that would impress any European visitor, who are used to forts and castles dotting their landscape.
The others are regretfully out of the way, especially for a tourist that are transit-bound. Since I live in Midtown, I would definitely suggest Science Centre and Aga Khan to people I would host, but the typical tourist is stationed in downtown.
The opening of the Eglinton Crosstown will be a game-changer in this respect I guess.
Canada's Wonderland
LegoLand
Depends on the tourist in question, if they are into amusement parks or not, if they have kids or not, and usually how much time they have in the city. These are day-trips.
High Park
Chinatown (spadina)
Greektown
Little Italy
I am sure they have parks and neighbourhoods wherever they are coming from. Chinatown is worth visiting but can be seen as an extension of a Kensington Market outing. The Distillery District is also worth visiting as mentioned by i42.
However, the Toronto "city-of-neighbourhoods" moniker is really overrated. You can appreciate the distinctiveness of each neighbourhood from a livability perspective as locals, but those nuances between Ossington, Little Italy, or Leslieville are surely lost on the average tourist.
For me, a true city-of-neighbourhoods is somewhere like Lisbon, where the neighbourhoods are genuinely distinct in built-form, architecture, eras, and sub-cultures, and also have significant landmarks in each neighbourhood.
I've never been.
Mink Mile
Woodbine Racetrack/Casino
Lol, no.
Though like it or not, the Eaton Centre is probably worth describing as an tourist attraction.
Seasonal:
CNE
Taste of the Danforth
Caribana
Pride
TIFF
Wet&Wild
Lots of other festivals and smaller museums I've left off but you get the idea.
No shortage of things to do in Toronto.
Anything seasonal + theatre + sports should go without saying. The attraction with all those events is that there is some activity to do + experience.
The problem as I see it is that there is a shortage of landmark attractions in Toronto. We certainly have lots of stuff to "do", but less stuff to "see", and the latter is important for sight-seeing tourism. On a day where one of those seasonal events are not happening or are unappealing to you (TIFF is not for everyone for instance), what can you go to "see"?
Yonge+Dundas Square certainly does not cut it. Honestly, neither does Nathan Phillips Square if it weren't for the Toronto Sign, City Hall, Osgoode Hall, and Old City Hall right there.
The Stackt Market is an example of something that while tacky, is a step in the right direction and would not mind seeing converted into something permanent. I have high hopes for The Well, Mirvish Village, and the BIG King Toronto projects as well. These three will provide more things to see and alongside the Stackt Market, will be very instagrammable (which like or not, is relevant for tourism in 2019). From a parks perspective, Ordnance Park will also be amazing for the views of downtown once opened.
Old City Hall should be converted into a Museum of Toronto after the court house relocates to the Ontario Court of Justice. City Hall should re-open their rooftop patio.
Finally, I cannot stress how much I want Ontario Place to be converted into a year-round, all-ages, tourist attraction.