It's always best to carry both passports. Enter Europe on your UK/EU passport, and enter Canada on your Canadian passport. Be careful when you leave Europe/UK to use the passport you entered with. If you show your Canadian passport they will hunt through it looking for the entry stamp.

Contrary to advice above, swith back to Canadian citizenship before you board, not in mid-air. Air Canada staff will want to see the passport you intend to enter Canada with. Otherwise you'll be swamped with questions.