Nobody is asking, and raising the sunken liner Costa Concordia is of little importance to the people of Williams Lake, but if I were asked this is how I would do it.
First I would view the Costa Concordia not as a giant, somewhat hollow vessel lying on the seabed; I would view the vessel as a unit with hundreds of cells, the cells being, of course, the empty rooms.
Most salvage companies will be looking to lay straps under the vessel and then attach inflatable air bags to these straps, inflating these bags, until the ship rises off the bottom sufficiently to be able to tow the vessel to some shore repair facility. There is no question that this system will probably work fine. The major problem with this kind of work is that the divers have to work in a deep and dangerous environment, and if the vessel is not secured properly it could of course accidentally slip into deeper water.
I, on the other hand, would start my salvage operation from the top of the ship. I would start by putting inflatable airbags in the above water room/cells. I would start here to ensure that as I inflated air bags in the rooms/cells below the surface that my ship would come up slowly rotating and floating to the level. My divers would not have to work in depths much below nine meters as they installed inflatable airbags in the sunken room/cells. The airbags in the above water level room/cells would have been inflated in advance of the start of inflating the airbags in the room/cells below the surface. Having secured and anchored my ship to shore, I believe that my method of displacing water in the room/cells with airbags in those sunken cells and advancing these airbags deeper into the ship as the ship rose I would be able to slowly lift the ship, far safer for both men and machinery than exterior airbags can do it. Un-inflated neutral buoyancy air bag packages of about two thirds a metre by two thirds a metre by two metres long could be placed in individual room/cells connected to an air distribution system and then inflated. The ship unencumbered with exterior airbags, now floating with inflated airbags in the individual room/cells, could then be safely towed to dry dock.