INTRODUCTIONIt is perhaps paradoxical that the prominence of borders and border controls in North America has sharply increased in an era otherwise defined by the breaking down of borders through continental economic integration. Indeed, borders and border control politics define the relations between the NAFTA (North American free trade agreement) partners.' What began as US drug and immigration control anxieties, mostly focused southward, have now been extended northward, as US border security worries have shifted in the post-9/11 era to focus on the potential entry of terrorists and weapons of mass destruction. The result, I argue, has been a partial of the US-Canada border and cross-border relations. In the aftermath of the terrorist attacks, Canada has experienced the kind of intense US political scrutiny and alarmed media attention that has long been familiar to Mexico. The politicization of the border has unsettled the traditional special US-Canada relationship and brought to an end what had been a mutually convenient low-maintenance approach to border control matters.The Canadian government has attempted to resist and reverse the Mexicanization process, making great efforts (with some success) to differentiate and distance Canada from Mexico. Yet despite how very different the two countries are in most respects, they inescapably have something profoundly important in common: both have a long and porous border that is increasingly viewed as a security concern by the United States, and both are increasingly dependent on keeping their border open economically. After the US border security crackdowns following the 9/11 attacks, Canada and Mexico have become more painfully aware of the risks and vulnerabilities that have come with asymmetric interdependence: they are far more economically tied to and dependent on the United States than the other way around, and thus are much more vulnerable to security-related disruptions in cross-border flows. This growing asymmetry, which has deepened and accelerated under NAFTA, is the underlying material context that structures their relations with the United States, limiting and constraining their policy options and giving Washington substantial leverage.2 In the following pages, I trace the changing practice and politics of US-Canada border controls, arguing that the politicization of the US-Canada border has taken on some of the characteristics of US-Mexico border relations. While enormous differences between the two borders remain, what is most striking (and most disturbing for many Canadians) are their growing similarities.DEPOLITICIZED US-CANADA BORDER CONTROLS IN THE PRE-9/11 ERAUS-Canada border controls during most of the 20th century can be characterized as low-intensity, low-profile, and a low priority.3 Border control issues rarely took centre stage in bilateral relations. This minimalist and low-visibility approach to border policing was mutually convenient and tolerated, and persisted into the 19905.4 The boom in legal commercial flows across the border in the post-NAFTA era overshadowed illegal flows, including the smuggling of drugs, cigarettes, migrants, and arms. The clandestine side of the expanding US-Canada trading relationship was largely kept out of the national political spotlight and never turned into a significant source of cross-border tension. Both countries exercised mutual restraint to avoid politicizing illegal border crossings while at the same time expanding and deepening cross-border law enforcement cooperation. Thus, at the same time as Washington frequently chastised Mexico for being the primary trans-shipment point for cocaine entering the United States, Ottawa quietly accepted the fact that the United States was the primary trans-shipment point for cocaine entering Canada (loud complaints would probably do little good anyway). Moreover, the United States was the primary source of unregistered arms in Canada, which many Canadians considered a security threat but grudgingly accepted as the price of living next to the world's largest arms producer-a country glutted with arms and regulated by much looser gun control laws. …