What happens if I sell shares to a buyer who then immediately winds up the company?

For a genuine, arm's-length sale, what the buyer chooses to do with the company afterward — including winding it up — generally doesn't reach back and change your own tax result on the sale itself. You disposed of your shares for agreed proceeds, and your capital gain (and any exemption you're entitled to claim) is calculated based on that sale, independent of the buyer's subsequent corporate decisions, which are the buyer's business, not yours, once the deal has genuinely closed.

Where this gets more complicated is if the buyer's plan to wind up the company right after closing was actually part of a pre-arranged structure designed around extracting the target's own retained earnings in a tax-favourable way, sometimes using the target's own funds to effectively finance the purchase. Structures along these lines have specifically attracted anti-avoidance attention from the CRA, and if a seller is involved in setting up or benefiting from that kind of arrangement, rather than simply selling to an independent buyer who later makes its own decisions, the seller's own tax position can be drawn into the analysis too.

The practical dividing line is whether the sale was a genuine, independently negotiated transaction, or a pre-planned structure built around what happens right after closing — get advice if it's the latter.