In Canada, the flight plan is a joint responsibility between the pilot in command ("in relation to an aircraft, the pilot having responsibility and authority for the operation and safety of the aircraft during flight time") and a flight dispatcher
This is called co-authority dispatch.
the shared responsibility of the pilot-in-command and the flight dispatcher for all decisions respecting the operational flight plan prior to its acceptance by the pilot-in-command, and for the flight watch
"[T]he operational flight plan is approved and recorded by the pilot-in-command and the flight dispatcher". (ibid.) The pilot-in-command alone cannot choose a flight path that the flight dispatcher does not also approve of. Each has veto power.
See more info here: Transport Canada - Flight Dispatcher.
The United States has a very similar joint dispatch responsibility system (FAR 121.533).
Around the world, there are examples where both pilots and dispatch have been given incentives to minimize the amount of fuel spent (pilot incentive, dispatch incentive).