I can only speak for Ontario. You certainly have identified a problem that has been identified in Ontario as a significant problem. We have had in Ontario, for about the last fifteen years, a government program now called the Family Responsibility Office. It's a department of I think the Ministry of Community and Social Services, and it seeks to enforce support and custody orders. But the volume of work is daunting and the compliance rates by payors still leave quite a bit to be desired, according to the press reports. But it's not an area where legal aid is actively involved in Ontario.
On October 31st, 2006. See this statement in context.