Can't speak to Canada.
In the USA, IRS rulings are that Bitcoin mined does not become taxable 'till you either sell it for cash or spend it on "tangible property" at which point it becomes taxable at the cash value of the amount of Bitcoin you spent.
There's a lot more verbage involved, but that's the short-form basic information you need.
I suspect state and local income taxes (where applicable) have to follow the IRS rulings on the subject.