Without going into detail, the greatest Burgundy I can imagine without getting highly unrealistic would contain all of the OTL territories+Lorraine, Savoy, Piemonte, all of the Frisias. Cleves-Mark, Jülich-Berg, Liège and a bunch of other minor territories here and there on the west bank of the Rhine.
If you go further into Burgundywank territory:
All of the above+all Imperial territory west of the Rhine+Provence and Champagne.
Expand it further than that and it can't really be called Burgundy anymore. I've said it before, and I'll say it again, but a Burgundy that contains all of France is not Burgundy; it's just a bloated France.