Where do modern treaty governments fit in? Are they similar to a federal government, provincial/territorial government, or more like a municipal government?
Well, all of the above.
The federation of Canada includes four orders of government:
Modern treaty governments are an interesting mix of the other three orders of government. They often manage huge territories, with responsibilities at international, federal and provincial/territorial levels, such as pan-arctic and regional wildlife comanagement (caribou, polar bear, salmon) for northern and Inuit modern treaties.
They also have local-level responsibilities to their communities like those of municipal governments, such as building and maintaining community centres, roads, water and sewers, and managing animal control.