Something like this..
Bush - 342
Sanders - 196
I'm not going to bother making a PV estimation, but it would probably be at least a 10 pt. margin in favor of Bush. States that Obama won by 10-20 pts. would be within 2-5 pts. for Sanders, due to more centrist Democrats reluctantly voting for Bush. Sanders' (relatively) far left policy positions would also allow Bush to run up the score in conservative strongholds like the Mountain West and the South.
Note: this is assuming a relatively normal campaign. Bush would probably have plenty of opportunities to paint Sanders as a far left loon, and if he capitalized on these opportunities, it could turn into a 1972-esque rout.
