There would be no tax on the gain if it was covered entirely by the Principal Residence Exemption. In Ontario, the value received by the spouse is governed by the Succession Law Reform Act and would depend on whether there are children. Under this law, the spouse is entitled to the first $200,000 of estate assets and a share of the residue, depending on the number of children. The spouse only receives the entire estate if there are no children.
That could affect the tax on the house (if the gain was not covered by the PRE) since only the assets going to the spouse could be eligible for tax-deferral. A good example of why we should be encouraging all clients to get their Wills in place.