Generally, there is no problem between Canada and the U.S. It's virtually an automatic exchange of information between the two. The problem is with other countries. The automatic exchange of information was suggested by the OECD in G-20, and turned down by the G-20.
There's another treaty, called the Joint Council of Europe/OECD Convention on Mutual Administrative Assistance in Tax Matters, with respect to collection, which Canada has signed but not yet ratified. Canada has to operate in the international context. The United States has the power to do it unilaterally. Canada can only act effectively internationally.