I live very near the border between the US & Canada - near Buffalo, NY.
The exchange rate between the 2 countries is now almost even - I think the US dollar is maybe worth 2 or 3 cents less than the Canadian, but I'm not positive about that. (Notice the use of the word US - and not American. Canadians are also considered Americans, as part of North America - and sometimes some Canadians take a little offense when we say something like: "How much is that in American dollars". Not always, but sometimes...)
I've taken the liberty of adding links to websites that might answer your question - and perhaps some more that you might not have known to ask.
http://www.necromantic.net/deadparrot/border01.html
http://gocanada.about.com/od/canadatravelplanner/qt/Money.htm
Just a warning about Canadian money, if you haven't been exposed to it before: it looks alot like ours in some ways, but decidedly different too. For instance - their paper bills are the same sizeas ours, but are colored - some people think they look like "play money". Their coins can be deceiving - there is something called a "loonie", which is a little bit bigger than a quarter and is brass colored, and it's worth $1.00. It's called a loonie because there's a pic of a loon (a duck) on the back. There's also a
"twoonie" which is worth $2.00 which is also a little bit bigger than a quarter but is worth $2.00. It almost looks like a half dollar with a penny inserted in the center. The rest of their coins look pretty much like ours and are worth about the same.
Have a great trip. Don't know where you're going in Canada besides the Falls - but Niagara on the Lake is beautiful, as well. You'll also be less than 2 hours or so from Toronto. Please don't hesitate to ask me for more info.
Gretchen