Although very different in many respects, the EU and Canada nevertheless confront common problems in certain areas. One such common problem is how to manage inter-state regulatory diversity within a federal (or federal-like), multinational system. This paper compares the different ways in which the EU and Canada have chosen to address the problem of national barriers to trade within their internal markets, and the consequences of these choices. It is somewhat counter-intuitive for EU lawyers that a full-fledged state may have an internal market that is less integrated than that of the EU; and yet that is the case in Canada. The comparison is illuminating as to the different possible approaches of federal polities to the problem of state regulatory choices and barriers to trade, the paramount importance of institutional choice, and the significance of historical and political circumstances.