Some decent information here, including illustrations:
http://napoleonistyka.atspace.com/French_infantry.html#_line_and_light
and the main page:
http://napoleonistyka.atspace.com/
If there isn't something clear, or still further questions, I too would suggest some of the Osprey books. Their dedicated search engine though, shows no books directly titled Fusilier or Voltigeurs, so maybe the Line or Light Infantry offerings have them included there. I'm sure I've some of these copies in my cellar, so let me know and I'll dig them out for a look.
Same linked site has info on the Prussians, but have to admire the work Peter Bunde has been doing. He has been producing 8x10 colour plates dedicated to the various regiments:
http://www.brigade-uniform-tafeln.de/
regards,
Jack