The list of currently supported cameras is here:
The new Canon Powershot G16 is not yet on the list, but the previous model Canon Powershot G15 is supported in Aperture 3.4 or later. So you have to wait for Apple to release a new raw support version.
While you are waiting, you have several options:
- Shoot raw&jpeg and use the jpeg as originals; you can switch this later to use the raw
- Or use the software that comes with your camera to develope the raw and import tiff or another lossless format.
Have a look at this page. Then you can get an idea, how frequently new raw support will be relased. The last release was sept. 16.