If there is more to it, please explain? Size of the prize must be worth their while to create an Ontario only DFS offering. Factor in the cut for the government, limited potential entry pool and prize money ,it may not make economic sense.
Books can offer different games and odds. I don't think igaming cares if DF or DK have a head start on DFS. The road to legalization was long. Competitors knew who where entering the market and gaps between offerings. Mgm, bet365 and others could have created their own version of dfs.
Books in the US can only take non-dfs action from within the operators state; however DFS is statewide. GTaking action from outside of one state is a federal offense, for the book and bettor, based on the wire act. Not sure if with a vpn, one can still run an account south of the border. Give it a shot.