All premium model cars are with can-bus system built-in, and many base model ones also come with can-bus nowadays, that's a difficult question of knowing if your car has can-bus or not, because this information is usually not listed in the user manual, and even some car dealers don't know if their cars have can-bus, well, if you want to know if your car has it, firstly let's take a look at what's can-bus.
CAN Bus is a multiplexed wiring system used to connect intelligent devices such as Electronic Control Units (ECU's) on vehicles, allowing data to be transferred in a low-cost and reliable manner. CAN means 'Controller Area Network' and was developed by Bosch in 1980. Most new vehicles use this system and it is becoming increasingly difficult to install after-market products without using a CAN Bus Interface.
If you have a Volkswagen vehicle, and you want to upgrade your factory radio and cd player with an aftermarket touch screen head unit with navigation system, there are many things you should know before buying aftermarket head unit, the first question you should know is if your car has can-bus or not, because if your car has it, you should choose the can-bus option as well for the aftermarket head unit, if not, the steering wheel control may not work or even you can not turn it on at all after installation.
Sometimes the seller for head units can tell you if your car has can-bus or not if you can send your car information to them, you can send your car's model, year model, and a dashboard photo, and sometimes they will ask you to find the information for your car.
If you still don't know if your car has can-bus, you'd better choose the can-bus option when you order an after market navigation system because it's not expensive, in case your car has it, then you can use it. The can-bus is usually connected to the power cable with a small white plug. Here is a picture showing how to connect the can-bus decoder with the power cable.
You can learn more information about can-bus from wikipedia: https://en.wikipedia.org/wiki/CAN_bus