Chicken and the egg… it’s not like we can run more trains and just aren’t. A tunnel would enable more service.
In an ideal world, we would run maximal, half-hourly frequency just short of the canal (as described by
@Northern Light )and send the few trains we can past. Across the network we see service cutoffs right where barriers begin; no need to let the canal limit service before trains actually have to cross it. A quick glance at Google Maps tells me that you can run to St. Catherine’s station without having to cross the canal. There is perhaps even room for one more station around Glendale Ave.
Sure, you can’t run all the way to Niagara Falls, but it gives every city before the canal much better service, building ridership to justify the massive expense of eventually crossing it.