My recommendation would be to use the Canadian passport, you should still take the Polish and German passports but focus primarily on one passport.

The middle name discrepancy could be an issue for the airline. As the airline will need to match your APIS data to the passport presented at checkin.

FYI, the airline will attempt to use APIS data (e.g. passport information) obtained from the outbound leg to the inbound leg. This could cause some problems when the return portion. If you utilize the Canadian passport for airline purposes and the EU passport for entry and exit to EU, the checkin desk may have additional question if the search your Canadian passport for an EU Schengen entry stamp. Again not a big deal but expect some additional questions.

Also, OP could you please post your flight routing. This would help answer your question as most people are assuming you are flying nonstop from Canada to Europe. You could however be connecting in the USA.