When I had to finish a chenille sweater I was able to get the same color (or very close) in a different yarn - not chenille. I would suggest the same fiber content (i.e wool, coton, blend) that the chenille is made with. I have not yet tried using thread, but I suppose that's a possiblity.
If it's a cotton chenille, you might want to stabilize the shoulders by stitching in a length of yarn the same width as the shoulder as you seam it. Cotton tends to droop & "grow" (what starts out as 2 inches past your waist in the morning, ends up mid-thigh by the evening). This works with most yarns that tend to "grow" (like alpaca, chenille, etc.)