I'm Colombian and need to know, if I'm going to travel from Colombia to Switzerland and transfer in Toronto, do I need a Canadian visa?
If you need a visa to visit Canada, then you need a transit visa to travel through Canada without stopping or visiting. This is true even if you are in Canada for less than 48 hours. There is no fee for a transit visa. You can apply for a transit visa by filling out the application for a visitor visa (Temporary Resident Visa) and selecting transit visa from the list of options on the form.
OOps, forgot to mention, Colombians do need a visa to visit Canada (an eTA if they hold a valid Green Card).
Yes, as stated by Timatic, the database used by Airlines:
The fact is, with the exception of passengers connecting to US-bound flights at Toronto terminal 1, Calgary and Vancouver, all transiting passengers will be checked by Canadian immigration - for this most foreigners need a visa or an eTA (depending on nationality)