Ok, I'll be the one to promote speeding
Brian's pretty correct though. Outside of rush hour and outside the Toronto area, 400-series highways are usually closer to 120. Hwy 21 will often see 110-120 from me, but only in good weather.
But you should be aware of our gestapo provincial police force (our version of state troopers). We have a new law in Ontario where they can suspend your license and impound your car ON THE SPOT at the side of the road if you're going 50 km/h over the posted limit. I'm totally serious, not a joke. They will leave you stranded, or at best drop you off at the nearest police station. Impound time is one week, minimum fine is $2K. Yes, this goes against due procedure (i.e. cop at the side of the road is judge, jury and executioner) but that's the way it is. Personally, even on an empty road, perfect weather, in a non-descript minivan I won't even push 40 over, in case the cop is having a really bad day. And they won't cut you any slack just because you're not local.
Oh yeah, they have aerial surveillance too. Because you see the police have solved all our other problems they can devote all this time and money to catching speeders. What a wonderful, utopian province we live in.
Seriously, though, be careful with your speed. And please don't judge our citizens by our police force and government!