Make Google Chrome Canary Default Browser

If you go to Google Chrome Canary preferences you'll see:

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Default browser
This is a secondary installation of Google Chrome, and cannot be made your default browser.

However, if you open up Safari > Preferences > General > Default web browser and click the drop down box you should see 'Google Chrome Canary' (obviously you'll have needed to install it first :P).

Seems to work for me.