An easier question is this - what's the legal limit of horsepower with a maximum output equalling 2000 watts?
2000 watts = 2.68204418 hp (via Google)
There is no TRUE CC to HP conversion, at least with kit motors and custom built MxB.
Your bike depending on tuning could be 15cc to 1 hp, or it could be 30cc - 1 hp.
You need to get into a shop that has a dynamometer and hit peak rpm, that'll tell you how many watts.