Urban infrastructure systems are critical to support sustainable and equitable urbanisation. Given the anticipated growth of cities in the future, infrastructure is becoming more prominent in urban spatial strategies as a means to meet planning goals. However, the fragmented governance and delivery of spatial plans and infrastructure projects create a challenging environment to embed planning goals across the planning, delivery and operation of infrastructure systems. Additionally, infrastructure planning faces uncertainty around future needs and the complex ways that infrastructures influence socio-spatial relations and political-economic processes. Fragmented knowledge of infrastructure, across a multitude of disciplines, undermines the development of robust planning strategies. Comparative analysis of strategic spatial plans from Auckland, Melbourne and Vancouver examines how infrastructures are instrumentalised to support planning goals, to better understand of infrastructure's multi-dimensional nature. Across the three cases, the analysis identified four common infrastructural modalities: rescaling socio-spatial relations through targeted intensification, intra-urban mobility upgrades and containment boundaries; re-localising socio-spatial relations to the suburban scale with 'complete communities'; protection of 'gateway' precincts; and local planning provisions to support housing affordability. Each modality mobilised infrastructure to support goals of global competitiveness, economic growth and 'liveability'. By examining infrastructure through a theoretical framework for suburban infrastructures, this analysis revealed the different ways in which infrastructures exert agency as artefacts shaping socio-spatial relations and the internalisation of political-economic processes. Findings suggest that stronger authority to control land-use and provide affordable housing is needed to meet the planning objectives in these city-regions. Additionally, spatial strategies should take a user-focused approach to infrastructure to meet the needs of diverse urban populations, and engage directly with the modes of infrastructure project delivery to embed planning goals across different stages.