They've tried walk on only ferries from Downtown Vancouver to Downtown Victoria and they aren't really profitable unless it's summer: https://www.timescolonist.com/business/v2v-explains-why-its-shutting-down-its-victoria-vancouver-ferry-service-4678241
This was direct between two tourist destinations, 3h one way trip $120 Adult, $60 Children.
Every year or 2 someone always floats the idea of Mainland Downtown to Island Downtown Victoria or Nanaimo
Just my personal thoughts given I suppose I could be subpoenaed as subject matter expert...
People generally don't like to take ferries. You basically have to be the only route to that place (so an island with no bridges), be vehicle ro-ro (so people can take their cars), or the trip has to be extremely long to take a car (like full driving days long). Ideally all 3...
Most of the foot passenger ferries that are able to run in North America are typically quick ultra urban as to be integral hubs to a mass transit system and have to be government subsidized. IF your transit system is any bit shit on either side, people aren't going to want to deal with taking a walk-on ferry. They are going to want to drive.
Realistically to take this ferry even with a 30min trip you have to account for terminal arrival and boarding, departure at St. Catherine's then getting in gear to go to Niagara [another 40min from what I'm seeing]. I mean the quickest in actual real world timings I want to say is a 90min trip... Driving is like 2h? [Correct me if I'm wrong]
Ask anyone if they want to drive in their personal car for 2h or take transit for 1.5h. You know the vast majority what the answer is going to be.