Based on my experiences in the Toronto area when my sister and I took a vacation up there, I think you could just take take the number on the "Maximum" signs, pretend it's an actual true maximum (instead of slower than anyone would ever go even if driving a cement truck), and stay just slightly under that speed in mph, and I think you'd be fine. If it says Maximum 40, just stay under 40 mph. No problem.
Or, as my sister put it, Canadians take their speeding very seriously. We literally had a school bus fly past us (on the right, no less) while we were going 10 km/h over the "maximum" on the 401. And heaven help you if you actually signal that you're planning to change lanes. The people in the other lane will move heaven and earth to close the gap and keep you out.