Fully-integrated groundwater – surface water (GW-SW) models are increasingly applied towards climate change impact analysis. Once deemed challenging to deploy because of data availability constraints, advancement in large scale, spatially contiguous physical-earth data sets makes these models feasible for more applications. Here we present a HydroGeoSphere (HGS) fully-integrated GW-SW model extending across the entire Nova Scotia catchment area. Covering 78,308 sq-km, including 21,195 sq-km of ocean, the model was assembled using open data from the Canada1Water (C1W) portal and serves as an example of how the national scale C1W dataset can support regional modelling applications. The model incorporates eight subsurface layers consisting of spatially distributed soils, and surficial and bedrock hydrostratigraphy. Importantly, it also includes a 10 km ocean bathymetry buffer, and while density dependent flow (DDF) is not currently implemented on account of large spatial scale, the model serves as a database of hydrological and physical data to support local scale modelling that will incorporate DDF. Currently, the model has been calibrated to daily transient conditions over the 2001 to 2020 time interval and has been applied towards mid- and end-century monthly normal simulations to project future SW flows and GW storage levels across the province. The climatological data used to force both the historic and future HGS simulations has also been obtained from the C1W portal. This presentation demonstrates application of the C1W data and modelling framework for conducting regional scale (i.e. sub 100,000 sq-km) SW and GW climate change impact analysis in continental Canada and Baffin Island.