LOT airlines (Star Alliance) is offering a great deal between Toronto YYZ and Stockholm ARN, connecting in Warsaw WAW for $526CAD. There seems to be excellent availability after September 1st.
Search on Google Flights, and book on LOT directly. LOT typically operates a Boeing 787 (Dreamliner) between Toronto and Warsaw. This books into ‘L’, and only earns 50% mileage on Aeroplan.