I see nothing inherently wrong with a Rob Roy type, or Hunter style, or Nightstalker type sporran made from canvas. It can be dyed to any colour under the sun. I have seen canvas shoes that have been painted to give a gloss or semi-gloss finish.

It doesn't have to look cheap and nasty. If made well, with care, I am quite sure that it would look as good as any leather sporran.

Regards

Chas