Canary is built every 60 revisions of Chromium. That comes out to be almost once a day. It doesn't go through a QA cycle. Dev Channel runs through QA and ships

Canary is built every 60 revisions of Chromium. That comes out to be almost once a day. It doesn't go through a QA cycle. Dev Channel runs through QA and ships about once a week. Beta just gets the stable release before stable does. But it's not coming down from trunk on a regular basis like the other two. The other important part is that Canary can run side-by-side with any of the other stable/beta/dev. So my preferred setup is running Stable and Canary side by side. (Disclaimer: I'm on the Chrome team, fwiw)