It is still a Canton system (Canton is just a brand like Bose or Harman Kardon etc) but just not as advanced as what can be found on the new Superb or Octavia 3.

Canton is a German manufacturer of loudspeakers, not amplifiers.

My S2 has Canton speakers even if it is just labelled as "Sound System".

I don't know which amplifier is used in the S2 as I've never ripped it out to check, but in the S3 it's an Alpine (or certainly the current batches of Navigation Pro aka Columbus are).

I wonder how easily they can be upgraded?

http://pages.ebay.com/link/?nav=item.view&alt=web&id=151793098575 ???