It's that, in practice, taxpayers are not going to provide the information. And there's already a similar question in the federal income tax return. Individuals are asked whether they own property outside Canada valued at more than $100,000. In practice, people who go to tax havens to avoid paying Canadian taxes are quite simply not going to answer that question. It's very easy to simply not answer, and the Canadian tax authorities have no way of verifying it.
On February 1st, 2011. See this statement in context.