Canada (Superintendent of Bankruptcy) v. 407 ETR Concession Company Limited, 2012 ONCA 569 has a useful summary regarding when an extension of time will be allowed:
 In my view, the extension of time ought to be granted. It is well established that in deciding whether to extend the time to appeal or seek leave, the court will consider:
a) whether the person formed an intention to appeal within the relevant period;
b) the length of the delay and the explanation for the delay;
c) any prejudice to the respondent;
d) the merits of the appeal; and
e) whether the justice of the case requires it.
See Rizzi v. Mavros, 2007 ONCA 350, 85 O.R. (3d) 401, at para. 16.