FlixBus stepping in to fill some gaps.
I've taken a look at FlixBus' services, and they are really taking the classic low-cost carrier strategy of avoiding terminal fees. Whereas the other operators depart from facilities such as Union Station in Toronto and St. Laurent Station in Ottawa, FlixBus is just loading from sidewalks without any facilities.
The one massive exception, is that they somehow secured a slot on Platform 15 at Guelph Central Station. That's a prime location, the one of the closest bays to the station building. I can only assume that the City of Guelph offered them that spot for free, based on how stingy they've been with their other stops.
Here are the combined schedules for 11 April 2022, also showing Rider Express and Megabus. If I've missed any other intercity bus companies on these routes, let me know.
Kitchener - Toronto seems well suited for travel
from Toronto to Kitchener, though not quite correctly timed for a full working day's commute. Seems like a good call, filling in the notable gaps in GO Transit's train schedule.
The single daily Ottawa-Toronto trips are simulateous with other existing trips from other companies. That may expalain why FlixBus is playing up the "express" non-stop nature of the route, in contrast to the existing offerings.
The Toronto-Niagara tmes are a bit more spread out from Megabus, but still largely redundant. FlixBus may actually have an advantage here in that their street-corner stop is in Clifton Hill near the touristy part of Niagara Falls, as opposed to Niagara Falls Station, which is in the old town centre.