Braucht man bei Flug – via Transit KANADA – ein Visum?

Yeah, you need.

“Passengers transiting Canada wants need to eTA or a visa, independent of the length of time in Canada

The only place where you should apply for eTA is on the official Canadian website! And definitely not on the abzock pages that were linked here zT.

The only official job to apply is the official Canadian page: https://www.canada.ca/en/immigration-refugees-citizenship/services/visit-canada/eta/apply-de.html