Both countries have a speed limit of 250 knots below 10,000', unless you're flying an airplane so crazy that it would be unsafe to operate it at a lower speed. In Canada the next speed limit restricts you to below 200 knots below 3000' within ten nautical miles of a control zone. In the US, it's below 200 knots below 2500' within 4 nm of the airport inside a class Charlie or Delta control zone. But in a class Bravo control zone, fill your boots at up to 250 kts. I'm writing Charlie out in full for the US version because that's how they say it (we say "cee"). That will maybe help me remember.
According to a document I read recently, the low altitude speed limits were established to reduce the severity of bird strikes, but I'm guessing that was just for the 250 kt ones, because I can't see that the birds would pay really close attention to which airspace they are in. The 200 kt speed limit is probably to help ATC control different speed aircraft.
Although the Americans have most of the same airspace letters as Canada, they don't really line up. They have class Bravo control zones whereas we only have class B airspace over 12,500'. If you pretend US Bravo is Canadian C you'll follow all the right rules, ensuring you have a clearance before entering the airspace. At 200 knots or below.