I believe if you search HBT or look in Brew Like A Monk you will find that Candi Sugar is just regular sugar in big chunks. I have also seen that the Belgian sugar may be made (or was made) from beets.
In BLAM it indicates that Candi Sugar is usually a liquid that has been carmalized to a degree and it is that caramalization that contributes flavor to a beer.
MATT - 65g in 2k8
3rd Circle Brewery
Ferminatin' - Route 666 Pale Ale
Figurin' to do - Oatmeal Stout, Gueuze, Belgian Blonde, Mild, English Pale Ale, Weizenbock