Don't do research because I already did it for you. If you're in Toronto for a day, try the following*: 

1. Start in Kensington Market, a diverse neighborhood with vintage shops and boutiques. Have breakfast at Fika Cafe.  
2. CN Tower: One of the largest structures in the world. It's taller than the Eiffel tower. Go early and make a reservation.
   Optional: Ripley's Aquarium - Toronto's city aquarium
3. Lunch: St. Lawrence Market - Toronto's main public market. Many eating options.
4. Nathan Phillips Square - Famous Toronto sign. Take a quick selfie and leave. 
5. Yonge-Dundas Square - Toronto's "Times Square"
6. Dinner: The Distillery District. A former industrial area revitalized by artists and pulsing with art galleries and restaurants.