erebos:
here are a couple of things to do:
first, click on a province
2nd, click on the church
3rd, look in the data box -- it will tell you revolt risk/month
4th, hover the cursor over the data w/ the revolt risk, it will, after a second or two, tell you the causes of your rev. risk.
types of causes of revolt risk:
religion: it may well be that you are not giving some provinces the religious toleration that they need. the way you modify your toleration levels is by clicking on your country shield, which shld give you the monarch ratings area, then to the right you shld see a shield w/ the religious icon, click on that & you shld see sliders representing each religion. unfortunately, it may be that you have four or more religions in your country, in which case some provinces are just gonna be unhappy. you may be able to release said provinces as vassals if you simply don't want to deal w/ it. otherwise, try converting some.
war exhaustion: this starts to go up radically after two years of war. it goes up more for provinces w/ different cultures than your state culture & it goes up more for provinces that are not part of your "core" nation. it may well be that you have not had enough peace. if this is the case, go to "peace" w/ everyone for a while. if necessary, buy peace. this can usually be done by offering 15% tribute, sometimes, however, you need to offer as much as 51%.
tax collectors: they add 3 revolt risk. this can be modified down by chief judges, which you can build when you reach infrastructure 4 -- not 3 as the manual states. chief judges reduce revolt risk by one.
nationalism: when you conquer a province which you don't have a "core province" shield on, you will receive nationalism revolt risk. it starts at 3% & goes down by 1 % every ten years. 3% is fairly significant risk, actually, since it checks every month, so you will have to expect some revolts. there is nothing you can do about nationalism.
cultural differences: + 1 at peace, + 2 at war. nothing you can do about this. as brandenburg you have german culture. if you keep the netherlands through all their revolts, you will earn dutch culture. as far as i know, this is the only culture you can "earn" in the game.
events: there is nothing you can do about events, you just have to wait them out. it may well be that your netherlands holdings are going through their want to create their own nation stage, in which case, you're right, it is their job to revolt & revolt often. if you hold on to them, you will have to put down numerous revolts until they finally "agree" to be a part of your country at which point you will receive dutch culture. you can also decide to release the dutch as vassals which will get rid of the problem.
eu2 is a very complicated game, but i'd give good odds on you coming to like it very much indeed if you take some time to get to know it.