That's what some legislators think, but this wouldn't be a cut-and-cover tunnel because of the water table. So there wouldn't be comprehensive replacement of utilities in the corridor.
A tunnel is useless to virtually every constituency but one: the owner of the mall on the lake, who wants cars from Pennsylvania to have unsignalized access to his front door. Putting aside the fact that Syracuse is a small city with no need for capacity improvements and no reasonable means of paying the enormous long-term maintenance costs of operating a tunnel, every tunnel plan ignores the local commuting needs: there's no realistic provision for a) an I-81/I-690 interchange or b) University Hill and downtown on- and off-ramps for I-81, because the expressway will necessarily be 200 feet below ground in that area. It's being proposed as, essentially, a driveway to the mall, public be damned.