The main question is, regardless of nationality and reason for travels, are travelers from the US allowed to transit through a Canadian airport (for <24 h and within the secure transit area) to a third country (EU)?
You may be permitted to transit through Canada to reach another country.
Where may could be interpreted in several ways. It also stipulates that:
You must follow all flight requirements and comply with any guidelines provided by the Airport Authority.
with a link to:
which links to a checklist that is very specific for people that actually want to enter Canada.
It feels safe to me to assume that, regardless of nationality, travelers from the US (and only the US?) are allowed to transit without completing any additional testing or checklists, with no visa or ArriveCAN.
Is this correct?