Excuse my ignorance, but why not just buy a cyclocross bike? They're the best suited for cross racing, no matter what level you're at. Also, given that you're a roadie, the position would be more natural for you.

If, on the other hand, you want a bike to cross train in the winter, get a mountain bike! Hybrid bikes are always compromises: you cant race mountain bike races with them, and you may not be able to race in a true cross race with them due to the bar configeration.