The Montreal metropolitan area has experienced many successive waves of immigration originating from a range of countries in the 20^th and 21^st centuries, and is home today to numerous communities of diverse origins. While assimilation theory expects immigrants gradually to adopt behaviours comparable to those of native groups in terms of residential location, the dynamics of this process may be different in the Montreal metropolitan area, which has historically been inhabited by large native Francophone and Anglophone communities, each with their own distinct patterns of residential location behaviour. This article aims to measure and analyse the residential cohabitation of people of immigrant origin with these Francophone and Anglophone host communities. The study population is selected from the National Household Survey of 2011 and is composed of the population living in households where the principal livelihood provider was born outside the country or has a parent born outside the country. For each of the fifteen largest immigrant communities we have constructed two regression models with, as dependent variables, the proportion respectively of 3^rd generation Francophones and 3^rd generation Anglophones living in the same district. This enables us to calculate standardised indexes of interaction according to a series of independent variables such as age, sex, length of residence, education, income and languages spoken. We find that in overall terms the spatial assimilation of immigrant communities takes place with reference to the Anglophone minority rather than the Francophone majority. However there is a high degree of heterogeneity both between and within communities.