...if it is needed?

I am looking to get an Alpine N333RRS sat nav system installed into my 2.0tdi A3 and I am not sure if I will need a can-bus unit.

Is there any reliable way to know for sure, or is it a question of having the wiring out and trying it to see if it works??

By the way, the cheapest place to get this sat nav unit appears to be Germany - and is almost half the price of some UK firms selling it. If you pay the German VAT, there is none to pay here when imported...