Does a corporation with only one shareholder still need an individuals-with-significant-control register?

Yes. The individuals-with-significant-control register requirement under the Business Corporations Act doesn't have an exemption for corporations with a single shareholder, and in fact a sole-shareholder corporation is often the simplest possible case: that one individual, assuming they meet the ownership or control threshold on their own, which they almost always will as the only shareholder, is the corporation's ISC, and the register simply needs to record them properly.

This surprises some owner-operators of small, wholly owned corporations who assume transparency-register obligations are aimed at larger businesses with multiple, layered owners. In reality, the size or simplicity of the ownership structure doesn't remove the obligation — it just makes identifying who the ISC is considerably easier than in a corporation with several shareholders, joint arrangements, or ownership through holding companies.

Even in this straightforward case, the register still needs to include the required details about the individual, not just their name, but the basis and timing of their control, and still needs to be kept up to date if anything changes, such as a new co-owner being brought in later.