While Latin America is undergoing a process of metropolitanization, we argue that intermunicipal cooperation (IMC) arrangements may serve as a quality check of the region’s metropolitan governance. We also adhere to the notion that IMC in a metropolitan region is affected not only by constitutional variables embedded in federalist arrangements but also in different ways. We test this assumption by building on a series of hypotheses taken from the literature on IMC. We then compare results from Mexico and Brazil, both federal countries with metropolitan regions. In testing the same variables, we observe different outcomes and a different explanatory power of the theoretical premises underlying IMC. We assign these explanatory differences to features of federalism, an understudied variable. We conclude that, while municipal drivers constitute relevant factors in predicting IMC within a metropolitan region, federalist arrangements modify the weight attributed to these factors.