Until he dies.
Of course he can petition the court in Canada to reconsider the child support order if his circumstances have changed.
But generally yes unlike in many US states - child support in Canada is a lifetime obligation.
Sort of like our entitlement programs paid by taxpayers, who pay whether they have children or not, right? So if he pays for life in Canada, do the children get any of his support money, or are they state supported for life?