Can your will be made to survive a future marriage?
The short answers are: if you are making a will in specific contemplation of a specific marriage, yes; if you are making a will which contemplates the possibility of some unknown future marriage, no.
Section 16 of the Succession Law Reform Act R.S.O. 1990, c. S.26 mandates that any will made before marriage is revoked upon the marriage, unless “there is a declaration in the will that it is made in contemplation of the marriage” [s.16(a)]. Note the “the”: while the issue is not a frequently-litigated one (coming up only a few times in all of Canadian law) what caselaw there is available holds that a will drawn up anticipating a later marriage must be in contemplation of a particular marriage. The language used in other provinces is almost (or exactly) identical to the Ontario wording.
“The section uses the words “the marriage of the testator” and “made in contemplation of the marriage”. The section therefore requires that the statement be referable to a specific marriage as opposed to marriage in general… […] The statement […] does not identify the marriage which was contemplated to take place after the execution of the will or the person he intended to marry. The case law is clear that contemplation of marriage generally is not sufficient. The statement must contain a reference to a specific marriage. […].” Ratzlaff Estate v. Ratzlaff,  S.J. No. 213 [Sask. C.A.] ¶ 31, 33. [Emphasis added; citations and footnotes omitted.]
“…the opinion is expressed in the Canadian edition of Theobald on Wills, 7th ed., at p. 52b, that no inference can be drawn from the nature of the disposition contained in the will to show such contemplation of marriage, if the declaration respecting a particular marriage does not expressly appear in the will.” Sedgwick Estate (Re),  B.C.J. No. 132 [B.C.S.C.], ¶ 3.
There does not appear to be an Ontario case directly on point. However, the counterparts of s.16 found in other provinces all contain similar or identical wording to the Ontario statute: it seems probable that an Ontario court would reach a similar conclusion. It would be difficult to argue that the Ontario legislature intended for the clause to include all future marriages when it used the word “the”; the indefinite article “a” would have shown such an intent and meaning, and could have been used, but has not.