In theory an appeal can be reopened after disposition - but it is a high standard to meet:
Chuang v. Toyota Canada Inc., 2016 ONCA 85:
 A party seeking to re-open an appeal after the appeal decision has been rendered faces a high hurdle. After more than 10 years of litigation, it would be unfair to permit the appellants to re-open their appeal on a different legal issue. In Mujagic v. Kamps, 2015 ONCA 360, 125 O.R. (3d) 715, at para. 12, this court said that the power to re-open an appeal "will be exercised sparingly and only where it is clearly in the interests of justice" (citation omitted). It is not in the interests of justice that this appeal be re-opened.
Of the Law Societies of Upper Canada and Nunavut