Sorry, I didn't realize you were writing from Canada.
I ride in Florida, so roads are flat. Having said that, a decent Cat3 rider can hold 27-28 MPH (45 Km/Hr) for about 45 minutes to an hour.
That can be pretty intense, so don't pay too much attention to your speed, and start racing in Cat5! It's fun, and if you're young enough, the sky is the limit with some dedication.