At a time of reassessment and possible retrenchment of domestic EIA requirements, this paper considers whether international law may provide a set of baseline requirements against which the adequacy and legality of Canadian EA law may be measured. The paper considers Canada’s international legal obligations to perform EIAs and how the implementation of that duty is affected by the constitutional division of powers over environmental matters. This examination is undertaken with the specific goal of considering whether CEAA conforms to Canada’s international legal obligations, and how the international rules may impact the exercise of discretion under CEAA. The conclusion of the paper is that the structure of transboundary EA rules under CEAA fails to implement international legal requirements in a number of important areas and, as result, misses an opportunity to strengthen transboundary environmental cooperation.