"like any other Perl 6 code".

No really, it's hard to tell, because Catalyst isn't ported to Perl 6 yet. Chances are that the dispatch information which is now implemented as attributes is handled with traits in Perl 6 (I remember a small web framework in Perl 6 floating around on IRC the other day that already did that), so an action method might look like this:

class YourApp::Controller is Catalyst::Controller {
   method someaction($id) is public</> {
       # executed if http://example.com/someaction is called
   }
}
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Maybe the dispatch code will have an option to use the build-in multi method dispatch, which is rather powerful and serves a similar purpose.

But until somebody actually implements it, that's all just wild guesses.