From 9 November 2016 on, you need a travel permit when you stop over in or fly to Canada. The permit is called "eTA", "electronic Travel Authorization".
How do you get an "eTA"?
According to the official website of the Canadian government, the "eTA" costs seven Canadian Dollar (CAD). Travellers are advised to apply for it before booking a flight, as the process may take a few days. Once issued, the permit is valid for up to five years or until the passport, with which you applied for it, expires. Within this period, you can travel to Canada as often as you want, but for a maximum stay of six consecutive months.
Rip-off on the Internet
Unfortunately, there are already some dubious providers who offer overpriced "eTAs". The Austrian Watchlist Internet warns that with such offers, you can't be sure if the permit will be valid and what happens to your personal data. It is there advisable to go the official way via the website of the Canadian government. You will find a step-by-step introduction there.
If you got ripped off or were victim of fraud, please turn to the next police station to file a claim.