I can tell you why as I know CBSA and CP too well.
Registered mail is not a priority to process for CBSA or Canada Post. It is a gamble on their processing time. I bought tons of stuff from Japan and shipped it to Canada by SAL. Some took 2 weeks to arrive, some took 2 months! to arrive. 2 weeks seems normal to me especially Vancouver is having a really bad backlog because of the fentanyl scare.
All I can say is, there is nothing you can do. You can try contacting CBSA, but they will just give you headache and might take weeks to respond.
Thank you @nosmas for your response! I really hope that it won't take 2 months!! But do you think it is in safe hands and it will somewhen be delivered or in the worst case returned to the visa office in Vienna? My biggest fear is really that it just disappears in a big black hole and never comes back. That would mean we need to request a new passport!!!!