There are no restrictions, you just need to tell your insurance its been fitted and they seem interested but don't care. They drive very different from what you'll expect and its a learning curve (short curve) . You can import from the US no issue, They need to be set up correctly so they don't push/pull your steering and track properly. The shop in Acton Ont, vintage cranks, are the provincial gurus on how they work/set up and some really good driving advice. All sidecars are not equal, personally I'd talk to them before buying anything, they are very approachable and helpful.
There is a guy in Newmarket making a beautiful car, but its about 12K all in, he builds for Indian.
I put a sidecar on a bicycle and found the steering confusing. What was happening was based on the two wheel principle that if you steer slightly in the direction you start to lean, the forces put you back to vertical.
With a sidecar even the crown of the road makes you want to turn to the right automatically as the vehicle is tilted. A half an hour in a empty parking lot was needed to unlearn two wheel habits.