Canonical refers to the church's public documents, those that are read aloud in the assembly, that shape the church's identity liturgically, and that the church will use for debate in its decision making about God's kingdom.
The difference between the canonical and non-canonical writings (like the gospels from Nag Hammadi) on, for example, the issue of women, is that the New Testament writings are functionally sexist, not ontologically sexist. I don't want to view women as the very root of evil or ignorance or betrayal. I'd rather say, "The Scripture writers made a mistake back then." We can work with that.
The real deficiency of the historical method as the only way of reading Scripture is that we cannot deal with the moral and theological inadequacies of Scripture historically; we have to deal with them morally and theologically. In other words, we need ways of engaging these texts that confront, say, patriarchalism, not by reconstructing a history that never happened or might have happened that we then make normative.
We don't put women at the Last Supper in order to have women priests. That's both bad history and really bad theology because whether one's a minister has nothing to do with who was at the Last Supper.
The question is: What has the Spirit shown us about gender? And in light of our discernment of God's will now, how do we engage these texts? History isn't going to get us there.
If we take only the good stuff in Scripture and don't take the tension with the bad stuff, if we take only "in Christ neither male nor female" and don't also include "wives be submissive to your husbands," haven't we in fact lost what is most valuable, that egalitarian ideals and hierarchical structures always stand in tension?