The Montney Play Trend (MPT) is a 1090 km2 region in northeast British Columbia that produces approximately one-third of western Canada’s natural gas output. In response to a proposed expansion of the MPT in 2016, the Government of British Columbia launched a Regional Strategic Environmental Assessment (RSEA) to identify the necessary conditions to achieve sustainable environmental outcomes. In this paper, we describe the methods and scenario planning tools that were developed to estimate how the development of the MPT might affect the subsistence economies of First Nations in the region. To demonstrate the utility of our approach, two impact assessments—Prince Rupert gas transmission pipeline and the Coastal GasLink pipeline—are presented. While no scenario can provide a definitive portrayal of exactly what will happen in the future, the tools that were co-developed are serving as an effective starting point for exploring possibilities that are at least consistent with current knowledge and can serve as a platform for collaborative learning and conflict management.