Can I roll my shares into a holding company before I sell to defer tax?

This is generally the wrong tool for the outcome you're describing. A rollover under the federal Income Tax Act lets you transfer property — including shares — into a corporation in exchange for shares of that corporation, on an elective basis, deferring the tax that would otherwise arise on the transfer itself. It's built for restructuring your own holdings, not for avoiding tax on an eventual sale to an outside buyer: moving your operating company's shares into a new holding company defers tax on that internal transfer, but it doesn't defer or reduce the tax that arises when the holding company (or you personally) eventually sells to a real, arm's-length buyer.

Where this kind of structuring genuinely matters is earlier planning, such as an estate freeze, or organizing a group of companies before a sale process even starts, so that things like the capital gains exemption can potentially be used by more than one family member, subject to each holding qualifying shares in their own right. Timing also matters a great deal here: doing this after you've already started negotiating a specific sale raises separate concerns entirely. Get tax and legal advice before assuming a rollover changes your tax bill on the sale itself.