Here are some things to help you get started if you want to make a fun memory and or go to a concert:
The Mill Race Folk Festival in Cambridge -
In Toronto there is Caribana; the Food Truck festival; Summerworks Festival (theatre shows in various venues); and Veld Music Festival.
If you want something a little quieter then you could:
Take a sketch book or a camera and sit quietly by the Grand River and photograph or draw what you see in nature.
Drive the Butter Tart Trail and decide for yourself which is the best recipe.
Decide what matters to you and choose to make each day matter. And, well, if you have three days then plan well and enjoy!!!!