There is a lot of info that can be provided with a bit more about you.
What size unit are you driving, what type of camping do you plan, how much time do you have, what are your interests?
The 401 is the major highway through southern Ontario. It is very, very busy getting from Niagara Falls to East of Toronto. You will want to chose the day and time very carefully when going through Toronto.
Are you aware of gas costs in Canada? Gas is much more expensive than in the US and particularly when you get into Quebec.
You should get lots of advice on this forum. You could also do a search for postings about Niagara Falls.