Can a minority shareholder demand their own valuation before agreeing to sell?

A minority shareholder generally can't unilaterally require the corporation to commission a valuation just because they ask for one, but nothing stops them from obtaining their own independent valuation at their own initiative and expense before deciding whether to agree to a proposed sale. Doing so is often sensible if a minority shareholder is uncertain whether an offered price reflects fair value, since it gives them an informed basis for negotiating, voting against the transaction, or raising concerns through Ontario's oppression remedy under the Business Corporations Act if the facts support it.

What a minority shareholder is generally entitled to as of right is access to relevant corporate financial information needed to make an informed decision as a shareholder, which is a different and more limited thing than being able to force the company to pay for an independent appraisal on their behalf. If the numbers being presented don't add up, getting independent advice early is usually worth the cost.