I began running Chrome Canary a while back due to some pretty slick improvements in the developer tools. I found out pretty fast that there is no way to set Canary as your default browser if you already have the public Chrome installed.

I stumbled across this tip somewhere but have long since lost the source. (hat tip to whoever first put this out there)

Simply open Safari, pull up the preferences and from there you can choose Chrome Canary as your default browser.