Just realized the city assessor's office was right about my basement reno and it cost me $3,400
Filed my permit in Calgary last spring claiming the finished basement wouldn't change my assessed value, and the assessor flat out said 'finished space is finished space, sir.' Two weeks after my appeal got denied I found out three neighbors in Dover had done the exact same thing and lost too, so save yourself the headache and just report it upfront.
Saw a thread about this on Reddit last year where a guy in Ontario tried the same thing and got hit with back taxes plus interest. The assessor always finds out eventually, might as well get ahead of it.