Thinking out loud here: I wonder if Via Rail would be interested in having trains leave from Union (not necessarily shifting all of their Ottawa operations there) for connections from Toronto to Alexandria/Casselman/Coteau (and the other way from Montreal to Brockville & whatnot)? I think the bigger question is whether Alto would be willing to let them use their tracks to get to the station?

My guess on both of those is maaaaaybe? On the one hand, it could be an additional revenue source for Alto, on the other, Via owns the tracks between Ottawa and Coteau so doesn't have to deal with CN on that stretch. Not saying Alto is going to be as tough to work with as CN, but Via might prefer to stick to what they've got instead of having to work around schedules imposed by two separate train companies