At the risk of sounding too absolute, no melodica sounds like a harp. You have to make them sound like a harp.
My favorite keyboard harmonica these days is an out-of-production Hohner Piano 26/27/32 series melodica with the sound holes on the back side. A Piano 26 works very well. They sound a bit dark. You will have to read my old posts to learn how I manipulate the instrument and amplification equipment to get a harp sound and modulations.
You should read the the notes that accompany my tracks on SoundCloud. Some of the technical information is described there.
Great song by Canned Heat. I have tried to get that harp sound myself.