You're onto something. There is, of course, the Saint John River, but New Brunswick residents are quite specific. We refer to Saint John as Saint John. Given that the commissioner's report is proposing to have Saint John the city represented by two members of Parliament, the understanding, or I think the perception out there, is that it's referring to the city of Saint John.
To finish my thought here, New Brunswick households and individuals are quite specific. When we talk about “the river”, we're referring to Saint John River. The St. Croix River is called “St. Croix” by the community. There is no confusion. Everyone knows what it is. It's the river that separates New Brunswick from Maine. If you say “Saint John” to a New Brunswick voter, they'll assume that you mean the city, not the river.
Even if the commissioners meant the river, I still think my objection holds in that there are still large parts of this riding that are far from the river. In particular, that's in the east of the riding: Sunbury County, which is south of Fredericton, as well as those four islands that I mentioned in the Bay of Fundy.
I'll also point out that even a reference to Saint John River is contentious, as currently there are campaigns by indigenous and other groups to rename the Saint John River as Wolastoq, which is a traditional indigenous name. In my opinion, it would not be wise for the redistribution commission to get involved in this debate on either side. Even renaming it Saint John to mean the river, I think, is entering a debate that is currently ongoing in the province.