At the moment we are using geojson from https://www.naturalearthdata.com via https://github.com/martynafford/natural-earth-geojson. There are different levels/styles available here but only states and provinces for North America, Brazil and Australia.
The underlying Plotly map uses CARTO for the actual map, we could explore this more: https://github.com/CartoDB/cartoframes, https://carto.com/developers/cartoframes/
Or find another alternative?