The scripture canon isn't actually mentioned in the canons of Nicaea. The early Church primarily used the Septuagint for the OT. 300 of the 350 quotations of the Old Testament aren't independent translations but taken from the Septuagint, the collection Catholics and Orthodox still use. All the early lists of the books of scripture include the same list.

The controversy *was* mostly over the NT .. well, except for whether or not to include the OT at all for a little bit early on. The only real controversy we see over the contents of the OT is with Jerome.