i have the GL1 and it's only so-so in very low light situations. the quality in general is excellent, but the few times i've shot at night without a camera light (using street lights for illumination), it was understandably dark and grainy.
apparently the GL2 has a minimum illumination rating of
6 lux (according to:
http://www.canondv.com/gl2/s.html). the nightvision canon cams are rated at 0.5 lux. and the XL1 is 2 lux.
i don't think you'll be as troubled as i was if you're still shooting in the daytime (even with heavy foilage cover). i'd shoot some test footage for ya, but it's raining, and i'd have to found a place with some heavy foilage for testing.