I've used some nice textured wallpaper to cover MDF baseboards, since it seemed an easy way to get a good texture in a short time and without the mess that is textured paint. Not exactly convinced by the result, but with some airbrushing or multiple layers of cloudy highlights, it could be done in a better way.
I assume that by "modgepodge" you are referring to some kind of wallpaper glue? I guess it could work on a canvas base, but I'd do a test beforehand to see if the glue retains some flexibility after drying - most wallpaper glues I've encountered dry to a rigid finish, and that could make it hard, maybe impossible to roll up the mat.
Finally, and that may be a continental problem, I've found that wallpapers over here only come in metric measurements (i.e. a bit above 500mm/20in wide), so getting a 2ft or 4ft mat will require lining up multiple bands. Covering up the joints might be tricky, although you could alleviate it somewhat by ripping the sides to produce an irregular edge.