In the Clark v. Clark (2016 ONSC 2381) decision, the Superior Court of Ontario dealt with the issue of over payment of support and the repayment thereof. The decision makes it clear that in such cases, the totality of evidence will be looked at with particular focus on the financial standing of the parties and the reasons for the same.
http://www.canlii.org/en/on/onsc/doc/2016/2016onsc2381/2016onsc2381.html