This is my guess.
1) Matt Hasselbeck
2) Josh Johnson
3) Pat Devlin
I'm not wild about Hasselbeck, but I think the Niners will look for a vet QB to groom an eventual Starter of the future. The choices of vet QBs that are versed in the WCO are pretty limited. Hasselbeck and McNabb are the only ones I see, and I don't see McNabb meshing with Harbaugh.
With Hasselbeck in the fold, the Niners draft a Devlin and trade for Johnson and see which one can be the starter in the future.