Contra Proferentum. Dunbar et al v. Ontario Gaming West GTA Limited Partnership
In Dunbar et al v. Ontario Gaming West GTA Limited Partnership (Div Ct, 2022) the Divisional Court (single judge) refers to doctrine on contra proferentum, though in not applying it in a Small Claims Court appeal:
 The principle of contra proferentem was applied by the Deputy Judge. I do not find that principle needs to be utilized in the circumstances of this case. I refer to the Court of Appeal for Ontario in Dunn v. Chubb Insurance Company of Canada, 2009 ONCA 538, 97 O.R. (3d) 701 at para. 36:. 2041219 Ontario Limited v. The Business Risk Management Review Committee
…Contra proferentem is a rule of last resort and will only apply “when all other rules of construction fail”: Canadian National Railway Co. v. Royal and Sun Alliance Insurance Co. of Canada, 2008 SCC 66 (CanLII),  3 S.C.R. 453,  S.C.J. No. 67, at para. 33, citing Stevenson v. Reliance Petroleum Ltd., 1956 CanLII 27 (SCC),  S.C.R. 936,  S.C.J. No. 68, at p. 953 S.C.R. [page 712]
In 2041219 Ontario Limited v. The Business Risk Management Review Committee (Div Ct, 2021) the Divisional Court addressed an attempt to import the contractual doctrine of contra proferentum into an administrative context (it failed):
 I also do not accept the applicant’s argument in its factum that the doctrine of contra proferentum applies. Again, the Court’s role is not to consider this argument afresh but to decide whether the decision below was reasonable. In this case, the Commission considered this argument and found that the doctrine did not apply because the Program was not established by contract but rather by the OIC. As stated by the Committee and accepted by Agricorp, “contra proferentum is a principle of contract interpretation and is not a principle applicable to the interpretation of an Order-in-Council”. This conclusion is consistent with the case law on this issue (see McClelland & Stewart Ltd. v. Mutual Life, 1981 CanLII 53 (SCC),  2 SCR 6, at p. 15), and is therefore reasonable.. 2249778 Ontario Inc. v Smith (Fratburger)
In 2249778 Ontario Inc. v Smith (Fratburger) (Ont CA, 2014) the Court of Appeal stated with respect to the rule that an ambiguous contract provision shall be read against the one who drafted it:
 Finally, the rule of contra proferentum applies in cases where the contractual terms are ambiguous: Consolidated-Bathurst Export Ltd. v. Mutual Boiler and Machinery Insurance Co., 1979 CanLII 10 (SCC),  1 S.C.R. 888, at p. 900 and Manulife Bank of Canada v. Conlin, 1996 CanLII 182 (SCC),  3 S.C.R. 415, at pp. 425-426.