Going out on a limb: I have an opportunity to purchase (for $20) the short shotgun microphone that comes with the Canon XL-H1. It's a mono/stereo mic, and it's described as in perfect condition. Here's one from eBay: http://www.ebay.com/itm/301859720875

Obviously, this kind of mic would not replace a Sennheiser MKE 600, or a Rode NTG-2 or anything at that level. I just find the built-in microphone the XA20 comes with picks up too much rustling noise each time I move the focus ring. But for $20, it may not be a bad option to use that shotgun instead as the default mic.

I understand that, this not being the Canon XL-H1 forum, a comparisson between the performance of those microphones (the built-in for the XA20 and the factory shotgun for the XL-H1) may not be possible. But I'm assuming this forum is more active than the other one.

So, any opinions on this? A good move? A "meh" one? Six of one half a dozen of the other?

It is a decent stereo mic for its price point, especially for $20, but it does require external power (5 VDC) that is NOT provide by the XA series camcorders. It is possible to make a power supplying adapter for it if you are sufficiently handy at electronic DIY, but probably more trouble than it is worth.

That mic was, I believe, used only on the XL1, XL2, and XL-H series camcorders.
And it is similar to one used on the old L1/L2 series Hi8 camcorders.(but the power and audio connector spacing is a bit different).

Oh, so it's more than just the jack adaptor, it's a voltage issue. Thanks for the info, I will let the mic go to another buyer.

Correct. As used with the XL series camcorders.

The 3.5mm stereo plug carries the left and right channel audio on the tip and ring. The sleeve carries the ground for both the audio and the 5 VDC power for the mic.

The 2.5 mm plug carries the +5 VDC at the tip. The sleeve likely does nothing. (The power ground return is via the 3.5mm plug sleeve.)