Obviously another advantage of the xl2 is you can use canon photo lenses of your choice. The lenses themselves likely cost a lot more than the camcorder body?
I have a GL2 and love it! It is a lot more compact and lighter weight than the xl2. In fact, I can't imagine putting a xl2 in a backpack with all my other gear..it would be pretty hefty and take up a lot of room in a daypack! I just looked it up and the Xl2 weighs almost 8 lbs.
If all you are doing is video the xl2 may be ok but if you are hunting, scouting, and carrying a bunch of other gear I'd likely pick the GL2.