I have personally not tasted Chateau Cantenac (I assume you are not speaking of the higher-end Boyd-Cantenac or Brane-Cantenac, but the lower-level St. Emilion). The lower level 2000's should be drinking nicely now, with the higher-end more structured ones needing more time. If you want to look at other's opinions try https://www.cellartracker.com/wine.asp?iWine=321170
Looks to me like it would be drinking nicely now. And BTW, its unlikely that its a 1L bottle you, not really the norm the area. More likely a 750ml or 1.5L.