I agree with the recommendations on Four Mile SP (low cost SP) and Brabches. (More of a resort).
I created a group in RVillage that may help https://www.rvillage.com/group/2617/niagara-falls-things-to-do-or-done.
Since you are coming from MD you might like to stop over in Letchworth SP, it was rated the top SP in the US! It's about 90 miles from NF.
Just a note, do not bring any guns or rifes with you, they are NOT ALLOWED, even if you have permits here, Canada is a foreign sovereign country with their own laws! Look up on line what can be taken into Canada and what can be brought back to the US.