It always amazes me that whenever I need to look up some uniform details, that my horde of books often doesn't cover the specific details I am looking for. In this case I wanted the details for the early uniform worn by the Guard Chasseurs a Cheval when they were part of the Consular Guard. Various texts went into infinite details of aspects of the imperial uniform with only a cusory mention of what went before. Dispairing I did what I was planning to do and used some left over Revell Chasseurs.
Depending on the context I'll use them as Consular Guard, ordinary Chasseurs or Guides as necessary.
Personally my best guess is that the actual uniform would have been the surtout (what was later the undress uniform) with a bicorne.