The idea isn't to divide the department but rather to create an organization, an agency. As was pointed out earlier, the francophone communities aren't sovereign. They don't have authority over immigration, unlike Quebec, for example.
One could imagine the provinces creating other entities. We know that candidates from the provinces function very well. Francophone immigration could be transformed that way. I think there are many options. Perhaps we don't need to implement them all at once because that would complicate matters.