If the HV-20 has Canon's AAS, the DM-50 is an option... Not the greatest microphone, but it does offer mono-shotgun (feeding both channels!), stereo-narrow (sort of stereo shotgun), and stereo-wide (rear quadrants appear as mirrored -- right-rear can sound like left-front)... Biggest advantage -- it fits the AAS so there is no cable needed, and power (if it is condenser, I didn't study it in that detail) is provided by the shoe.

Most of my shooting with an Optura 40 is done with it. My XH A1 gets a $500 Audio-Technica with dual XLR outputs (and a jury rigged clamp -- the XH A1 has 25mm/1" clamp but the AT is 21mm; I had to fit a rubber spacer from a handle-bar mount adapter). The AT can fake the mono mode by setting it to unmatrixed mid/side, using the mid for channel 1, and setting the camera to duplicate channel 1 to channel 2. (the stereo modes are similar to the DM-50)