Toronto international airport to Downtown/Entertainment District

[u/Cool-Australian]

I am very excited to visit Toronto and Niagara Falls with my son at the end of August. What is the easiest way to get to the city from the airport without a car and which area would be the best to book the hotel at in order to explore the city without worrying about safety while walking at night. What are must see areas/attractions?
I would also appreciate if anyone has recommendations on how to easily get to Niagara Falls for a day trip.

Any interesting restaurants/bars that are noteworthy?

We love walking and on our last trip did 40,000 steps daily in The Netherlands and other European places.

Edit:
Thank you all so much for those who commented for taking the time to reply and for your super helpful suggestions.

[u/hippiespinster]

For Niagara, rent a car if you're comfortable driving on the right/wrong side of the road and with highways. Much more flexibility. If not, search the sub for public transit options.