Upvote:6
According to Canadian Government site, you will need a visa in advance if you hold an alien's passport:
Note: Holders of Alienβs passport and Stateless individuals need a visa to visit or transit in Canada.
Another page (Transit Without A Visa) states the following:
All nationals who qualify for the TWOV program must also meet these conditions:
- They hold a valid passport or travel document issued by the country of which they are a citizen;
This does not include you, since the alien's passport is issued by Denmark, which is not your country of citizenship (that's clear because you hold an alien's passport).
Bottom line, visit a Canadian embassy/consulate to issue a transit visa in advance.