Hay Marco
There are no tolls except on the 407 and you won't be going on it unless you choose to (it runs north of the 401 from around Missisauga into Durham Region east of Toronto). And if so, you will get a bill in the mail in a few weeks or so (they take a picture of your plate and mail the bill, there are no stops on the highway itself). It is a per km charge so the farther you go on the highway, the more you pay, but it isn't overly expensive, but if you go in around rush hour, the charges are more.
Here is the website if you want more info before you decide to use it or not. I don't like to use it because I'm a cheap bastard but I do occasionally because it can save a LOT of time vs the 401 at certain times of the day and depending on how far across Toronto I have to go.
http://www.407etr.com/Just to give you an idea ... If you did the full 107 kms on a weekend, it would be around $25, weekdays in prime time, about $31, that's Canadian currency, but depending on traffic on the 401, it could easily save you an hour or more on driving.
If your coming from the East you won't be near it, if you come from the West it is an option route or you can stick with the 401 thru Toronto. Just take a look on mapquest and you'll clearly see the 407 highway north of the 401 and Toronto). As far as i know, EXpass is only for the border crossing, definitely not the 407.
If your thinking of your round the lake trip and you do it from East to West, they you will not need to hit the 407 at all, if your coming the other way, I would seriously consider it, depending on your timing, of course.