Can a minority shareholder block a sale that the majority wants to go through with?

Generally, no. Most significant corporate decisions, including a sale of all or substantially all of the corporation's assets outside the ordinary course of business, require only a special resolution passed by the required majority of shareholders entitled to vote, not unanimous consent, so a minority shareholder typically can't unilaterally block a properly authorized sale.

A minority shareholder's protection lies elsewhere. If the sale, or the process leading to it, is conducted in a way that unfairly disregards the minority's interests — for example, through a lack of proper notice, inadequate disclosure, or a price structured to specifically disadvantage them — Ontario's oppression remedy under the Business Corporations Act allows a minority shareholder to ask a court for relief, which can include an order affecting the transaction itself in serious cases. This is a fact-specific remedy, not an automatic veto, and a minority shareholder considering it should get legal advice promptly, since delay in raising concerns can affect what a court is willing to do.