Is This Realistic? Toronto Friday/Saturday + Niagara Falls Sunday

I’m planning a weekend trip and wanted to get some feedback from people who know Toronto and Niagara Falls better than I do.
The rough plan is:
Friday Evening (arrive early evening)
CN Tower
Royal Ontario Museum
Casa Loma
Toronto Islands
St. Lawrence Market
Obviously I won’t be able to do all of these Friday, so I was thinking of doing 1–2 attractions Friday evening and saving the rest for Saturday.
Saturday
Spend the full day in Toronto
Visit the remaining attractions:
CN Tower
Royal Ontario Museum
Casa Loma
Toronto Islands
St. Lawrence Market
Sunday
Drive to Niagara Falls
Spend the day exploring the Falls before heading home
A few questions:
Is this itinerary realistic, or am I trying to cram too much into one weekend?
Which Toronto attractions are absolute must-dos, and which would you skip if time is limited?
Is Toronto Islands worth the time if I’m only in the city for about a day and a half?
How much time should I plan for Niagara Falls on Sunday?
Am I missing any must-see attractions, neighborhoods, restaurants, or experiences?
Any tips for parking, public transportation, or avoiding long lines?
For context, this would likely be a summer trip.
Thanks for any suggestions!