One of the main goals of a tax treaty is to prevent tax evasion. The treaty sets out information-sharing mechanisms under which the Canada Revenue Agency can approach tax authorities in each of the three countries and request information on any taxpayer suspected of failing to meet their tax obligations in Canada. So there is a mechanism in place insofar as the agency has good reason to believe that Canadian taxpayers are not complying with Canadian tax laws. The agency can approach each of these countries. The government's policy is expected to include the most recent version approved by the OECD on the exchange of information. That is an important objective of tax treaties.
On October 4th, 2010. See this statement in context.