The official policy of Sixt at ZRH is:
The lessee and the driver must present a valid driver's license and an identity card or passport while receiving delivery of the vehicle.
Driver's licenses from non-EU countries (except Switzerland) are accepted if:
a) no visa has been entered in the passport.
b) the customer has a visa in his passport and at the time of hire has not been in Europe for longer than 6 months. If he has been in Europe for longer than 6 months, he must present a driver's license from an EU country.
Driver's license printed with non-Roman Alphabet (Arabic, Chinese, Japanese, Cyrillic, etc.) must be complemented by an international driver's license.
For driver's licenses from countries not part of the international driver's license treaty, an official translation of the license must be presented with the original license.
Bottom line, you shouldn't need an IDP at ZRH with a Canadian driver's license. Safe travels!