To my knowledge there isn't a PC-based map editor for GBW2, but if you have an emulator and a GBW2 ROM you can post your map by pasting together in-game screenshots. Maps for GBW2 go here.
To my knowledge there isn't a PC-based map editor for GBW3, but if you have an emulator and a GBW3 ROM you can post your map by pasting together in-game screenshots. Maps for GBW3 go here.