Although municipalities across Canada have adopted principles of new urbanism, smart growth, and sustainability in their planning and policy documents, new suburbs continue to reveal the influence of conventional development practices. This paper examines challenges to implementing new planning principles and reveals some of the ways that the development market selectively resists planning objectives in three Canadian urban areas. Interviews with planners, councillors, and representatives of the development industry indicate that, while land cost pressures contribute to increasing suburban densities, developers may challenge planning principles related to urban form and function. The study finds that weak political commitment and market pressures frustrate planners’ desires to create accessible and open communities. Conceptual distinctions between planning approaches important to theory become blurred in practice.