In order to AMA Link Canon C300 footage, you need to install Canon's XF Plugin 64 for AMA (2.0.3 in my case I'm on MacOS 10.9.4)
Canon XF Plugin 64 for Avid Media Access 2.0.3 [Mac OS X]
Available here:
http://www.usa.canon.com/cusa/professional/products/professional_cameras/cinema_eos_cameras/eos_c300#DriversAndSoftware
It will appear as MVP_Canon X64 2.0 in the Console (AMA_ListPlugins)