I played my first game with Netherlands, And i also had some trouble getting the rebels state to the south back under my control.
As Darkrenown said, I got along with belgium in the SoI of Great Brittain. I focussed on becomming a great power myself. Took a few years but that worked. by that time I think Belgium got removed from GB SoI and there was only an alliance left between GB and Belgium. Got around that by declaring on denmark, also Belgiums ally.
Before I could make my move on Belgium France pulled them into there SoI and I had to get them out of there first. Managed to do that. and a year later Belgium lost its alliance to France aswell and it was for me to grab, finnaly.