I don't have the link, but in another thread someone illustrates the statistics on current franchise QBs and the round they are taken in. Besides Tom Brady, all franchise caliber QBs were taken in the 1st and 2nd round with Brees and Favre being the only 2 in the 2nd.
That being said, if the Bills do draft another 3rd rounder like Edwards, I think there isn't much hope for him to become a franchise guy. This doesn't mean he will be terrible, just not the long-term guy we all want.