Also make sure the rental car agency knows you are taking the car into Canada. They are used to it but you need to tell them so they include the Canadian Insurance card.
The Olde Angel Inn at Niagara-on-the-Lake Is an original pub that is nice to see.
Niagara-on-the-Lake Pub The Olde Angel Inn, Restaurant and Live Entertainment
If you are flying in, driving to Niagara on the Lake, doing a winery, then driving back to Niagara Falls it will be a long day. It can be but I hope you won't be jet lagged.
There is a glass blowing factory in Niagara Falls Canada that is nice to visit.
https://www.niagarafallstourism.com/.../angelo-rossi/