Of course he can. His team is weak enough and his tactical sense (or self confidence) may get him to make mistakes. I'm not saying he won't win but classics are unpredictable, everything can happen. Where was Vansummeren before his win in Roubaix? Nowhere.
The only ones with a strong team are Boonen and Gilbert and there are some justified doubts about their shape. I want to see Cancellara getting another monument, don't care which one. Then, on the dreamland, Hushovd winning Roubaix.
Sagan can wait until Amstel to win another big one, he has plenty of time ahead of him, no need to upset the old men

Anyway, regarding Ronde Van Vlandeeren, Cancellara looks to have the edge on the climbs like Kwaremont but if Sagans hangs on (like Boonen last year), it's almost impossible to drop him in the flat and impossible to outkick him on the sprint. Looking forward to Sagan vs Boonen vs Cancellara with some outsiders like Haussler, Chavanel, Terpstra, Boom,etc. The best chance Boonen has (just my 2 cents) is using his team on breaks (not with Vandenbergh as their sprint hope) and having the others chasing them down while he's riding on wheels.