Certainly in Quebec a number of public transit systems are already being used to nearly full capacity. I think the situation is similar in the rest of Canada, which means that without more infrastructure, it will be difficult to increase the number of passengers.
In any case, it's a question of accessibility. If the infrastructure is not in place, people can't use it. That is clear.
I would make the following distinction, however: both are important to the extent that building infrastructure does not automatically come with the funding to operate it. This raises an entirely different issue that often needs to be addressed.