Can't import photos from G15 to Macbook Pro!

Did you install the software that came with the camera?  It may be the software is different than your EOS software.  I don't know, since I only own an A620, a G9, and G11.  I do know that I used to have the same problem as yours with my G9 and my new iMac three years ago.  It also ran Lion.  Canon eventually updated their software (see the website to download updates), and then I was able to connect my G9, as well as G11 and A620 to the iMac via USB and transfer images.

Dennis