Make sure your unvarnished kayak is is not sitting in the sun all day. Try a little 2ft area of varnish. sometimes the cloudiness you see is the surface not having a smooth gloss coat on it.

This is why plexiglass is not used for windows. Eventually it clouds from dust in the air hitting it. As hypothetical as that sounds, it's true. This is why varnish needs to be refreshed - not just from the sun.