I'm having a hard time digging up these specs. The Canon website lists the following specs for these various cameras.

XF300: 2-Channel, PCM digital recording, 16-Bit; 48kHz
C300: Linear PCM; 2-Channel; 16-Bit; 48kHz
C100: 24 Mbps Mode: Linear PCM; 2-Channel; 16-Bit; 48 kHz (i'm guessing this means while in 24mbps video mode)
5D Mark III: Linear PCM
7D: Linear PCM

Some cameras don't even have any audio specs, and just list H.264 for video.
When I import my 7D footage into Premiere, it says: Source Audio Format: 48000 Hz - 16 bit - Stereo

So, does this mean that the DSLR's record at the same audio data rate as the XF300, C300, and C100? I understand the preamp's suck, that's a different topic and I can get around that with my juicedlink box.
The question is, do the Canon DSLR's record at uncompressed PCM audio, 16 bit, 48KHz? The Canon website is light on specs for the DSLR's and I'd like to get some confirmation from someone who knows about this.

Thank you!

According to Vegas Pro 12, my 550D clips' audio is:

48,000 Hz, Stereo, PCM

So assume that the audio is uncompressed PCM. I doubt that the A-D hardware is particularly good for the video bolt-on capability - it probably matches the sub-standard video scaling and AVC coding quality. As you say, the pre-amps aren't up to much.
I suspect that the XF series has far better audio front ends as they have balanced mic inputs and their sound quality is acceptable to major broadcasters. In addition, their 4:2:2 MXF format is effectively an industry standard so the sound would match the video quality to be accepted into a professional production workflow.