No one is really arguing the viability of the line more than the obvious political gift that the line is in light of many other projects that have priority over Peterbrough i.e. Go Bolton line. Unlike Europe, North America doesn't have much of a rail culture and history.Well of course a bus service would attract a lot fewer riders, for the same reason a streetcar line attracts more riders even if it's not any faster than the previous bus. Rail attracts more riders. Not to mention a bus to the Oshawa GO station, then GO train downtown would probably take twice as long a VIA train the whole way. If the track is improved, flag stops eliminated, and the ride is faster and smoother than the previous VIA line, ridership and financial performance will be vastly improved. Only in North America would the viability of a 120 km rail line to a metro of 117,000 be in doubt.
I remember visiting my grandparents in Italy in a town of 1000 people max and being able to catch an express bus (akin to go/Greyhound) to the nearest mid size town (pop maybe 30 000) and from there being able to catch the train to the regional capital and/or elsewhere in the country. Southern Ontario doesn't have anything close to this set up. Now if we did then I can see Peterborough as being an extension of this system.
I think a truly forward thinking federal government would have tabled the long talked about HSR link across Ontario/Quebec instead of this vote buying Peterborough line.