Has anyone had experience overstaying the 90 days or leaving on a different passport than you entered on?
Since you are a Polish citizen I can't fathom how overstaying would apply to you. What are they gonna do? They can't throw you out of Poland. In Poland your Canadian citizenship will be of secondary importance - if any at all.
Also, I don't think there are any restrictions as to what passport you're using to leave Poland. There used to be some issues with that in early 1990's but not anymore. What they may check at the airport is whether the passport you hold allows you to enter the destination country.