If you have an alpha channel on your original animation, it would be easiest to use an Alpha Track Matte to accomplish your matte. If you don't, it would still be wise to go back and generate a matte pass for your animation. If this isn't possible, then you could always key out the background if it's a solid color, and then use the result as a matte for your highlights.
im using a 2d animation i made in flash not cg1 i want the reflection of the sun to com off the character
Yes, paint it in Flash. or use masks and e.g. the Stroke effect combined with a blur in AE.