Wiring – Acceptable locations for junction boxes in a kitchen

You will need to refer to the documentation that came with your new appliance. Is it rated to be connected with a cord an plug or directly wired?

To start with you will need to run a new cable of 10 gauge wire and replace the circuit breaker in your panel. Operating the appliance with 12 gauge wire when it is rated more than 20 amps and requires 10 gauge wire violates the manufacturers instructions as well as overloading the circuit.

I have never liked the idea of hardwiring undercounter appliances with or without a switch. I am assuming that the dishwasher is on its own circuit. Since you don't seem to mind putting a switch at the location shown. Why don't you just put the GFCI at that location and feed through that device to a standard receptacle behind the dishwasher? It's pretty simple and has been described many times on this site, or there are a set of instructions on or in every box the GFCI comes in.

If you don't like the idea of adding a receptacle, you could just add a GFCI breaker to that circuit in your panelboard.