Here is the supported cameras for tethered shooting Knowledge Base article:
http://support.apple.com/kb/HT1085
The 7D is not listed. If you'll note, no recent Canon cameras are listed. This is because the Canon cameras used to support a standard tethering protocol, and they have removed this support. Apple implements the standard protocol, but does not have code to handle the new, proprietary Canon protocols. As such, you're unfortunately out of luck and will have to tether using Canon's software and then use a hot folder to auto-import to Aperture (you can do this easily, with scripts and with Automator, and it is in the documentation).
It's unfortunate that Canon removed this support, and unfortunate that Apple didn't have the resources (or maybe the information from Canon? I don't know) to do this, but that's what you have for now.