I have a passport from Finland that is expired. I used it last year to obtain an ETA. This year I need to travel to Canada and don't have time to renew the passport. Can I use my other passport issued by Philippines and bring that to the airport for boarding a flight to Canada? Philippines is not a visa exempt country. Will I be allowed to board the flight with an ETA issued to a different passport?
1) When you provide the expired, therefore invalid, Finnish passport to the check-in desk and they scan it, it will be instantly rejected by the system as invalid.
2) When you then provide the valid Philippines passport, they will examine it for a valid visa and reject it. Scanning it would also probably result in a "no board" outcome by default.
The combination of a valid passport
and it's electronically linked eTA is what would have resulted in a "board" confirmation from the check-in system, if an eTA is attached to a valid passport.