Yes, one could rely on other sections or common law defences. However, we can't answer your question in an absolute manner given the existence of section 43.
In a way, this is the point that Judge Arbour made in Canadian Foundation for Children, Youth and the Law. Other defences might apply, but, since section 43 exists, it's hard to know how far it would actually be read down. As my colleague explained, this is an escalator defence: If section 43 doesn't work, you look for other defences. However, since there's been little development in the case law, it's hard to know to what extent other defences might apply. It's relatively clear in the case of the de minimis principle, for which there's a test. The same is true of the necessity principle. In addition, as I said, the implied consent defence, which is used in common law, could apply in certain cases, but that would require further case law developments.