Do the math.
A train cost $600 an hour regardless of it size and can carry X riders. A train can do a round trip in x time depending which line its on and where its going.
A bus can carry 80 seated using DD buses at about $200 an hour. Its round trip could be 2-3 times longer than a train depending on the time of day it travels and where.
To find out the numbers of riders needed for each service, you need an average fare to cover the various stop to help you to arrive at an 85-100% cost recovery ratio. You divide that fare into the hourly cost to see what the numbers are needed.
In most cases, there isn't enough bus riders on various routes to justify the needs for a train in the first place.
From the few times I have travel to/from Kitchener, it is a hit and miss point to cover average cost ratio and that various from the time of day as well the day of the week.
All cost are based on a min of 4 hours of service.