I expect that integrating the ticketing process with airlines would bring a noticeable boost in ridership. The actual price probably isn't that noticeable given how expensive plane tickets are though.
Out of curiosity, I examined the Kingston to Pearson trip to see how the train compares other modes for people getting from eastern Ontario to the rest of the world.
Kingston - Pearson: Wednesday June 17 2015
Megabus: $58, ~3h30, 3x per day
VIA (Escape) + UPX (Presto): $66, ~2h55*, 14x per day
*2:15 VIA, 0:07 transfer, 0:08 avg wait, 0:25 UPX
Taxi/Car: $$$, 2h35 with no traffic (as if!)
Air Canada: $237, ~1h00 + security, 5x per day
So the train looks like a fairly competitive option that many people would probably choose if it were an option on online booking sites.