I think you have to look at the comparative population densities and how it is distributed. The US 'northeast corridor is around 50Mn. The Chicago Metropolitan area ('Chicagoland') is comparable in both population and area to the Greater Golden Horseshoe Area, and some of its included communities are significant industrial areas, ports, etc. in their own right. They aren't just bedrooms feeding the centre (OK, we have Hamilton).
They also have state funding of AMTRAK.
The US is slightly smaller than us in area but has ten times the population. At least on both coasts, they don't have to deal with the concept of multiple hours between major population centres.
In terms of population density and distribution, southern Ontario and Québec are far superior to the U.S. Northeast. In Canada we have a lot of suburbs, but at least we don't have much exurbs.
Open up Google Maps and zoom into any spot in the Northeastern U.S. which appears to be an undeveloped area outside of a city.
Chances are you will actually find houses scattered arbitrarily across the landscape.
Now do the same in Canada.
Chances are you will find farms or forests. The houses which do exist are either grouped into hamlets or are former farmhouses.
So while the population of the Northeastern U.S. is far higher than southern Ontario/Québec, a shocking number of them are living in single-family houses randomly scattered through the countryside. Those people would be nearly impossible to serve using anything other than cars. At least Canadian suburbs are built at a sufficient density that there can be some basic transit service, and a reasonable chance that there is a grocery store within cycling distance.
Keep in mind that it not only matters how many people/destinations are accessible from train stations, it also matters what percentage of people/destinations can be reached. Because in order for a trip to be served by rail, the origin AND the destination both need to be accessible, it's not good enough to just have one or the other. In the U.S. if there are residences or destinations accessible by train, there is a much higher chance that the opposite end of their associated trips is not reasonably reachable by train/transit, making those land uses much less relevant in the calculation of potential rail demand.
In other words, the potential rail demand generated by a given building near a train station in Canada will be higher than an equivalent building the same distance from an equivalent train station in the U.S.