Beating France as Spain?

So I really am a noob in eu4 (less than 50h). I'm playing as Spain (on easy to get the hang of the game) and France was my ally from the start, but they recently got interested in my colonial territory and broke their alliance with me. At the moment they have 0 manpower and smaller army (a little bit). Also we are paired up on mil techs and they already have elan and about 5 offensive ideas (I have 1 offensive idea). Can I win a war against them, and if so, what do I have to do? People say France is really tough, so I'm quite afraid