Coastal ecosystems naturally adjust to rising sea level by migrating landward. However, in areas subject to accelerating sea level rise and sedimentary deficits, natural (e.g., cliffs) or artificial constraints (e.g., roads or defense structures) along coastlines can limit this mitigation. This process, known as ’coastal squeeze’ can lead to a reduction in the surface area of a given ecosystem. The present study evaluated the potential migration distance of coastal ecosystems in the St. Lawrence Estuary and Gulf (Canada), to determine whether they have the space to move landward with sea level rise. The results revealed that 57% of sandy and salt marsh environments, have a migration potential of less than 30 m. In over 50% of cases, artificial constraints are likely to limit this movement, and more than 75% of these constraints are located within less than 30 m of the upper limit for migration. The impact of coastal squeeze is of concern for both sandy and salt marsh ecosystems, which occupy 74% and 26% of the coastal area, respectively. To enhance the resilience of coastal ecosystems in the St. Lawrence Estuary and Gulf to environmental change, it will be important to start addressing the conservation of sufficient accommodation space for their landward migration.