The trick about buying or renting in Ottawa is to plan for subsequent postings there. If you buy a place that is convenient to your first job, you could be screwed if you get a second (or third) posting within Ottawa and your new building is not as convenient to your home as on the first posting.
I can't imagine why anyone posted to Ottawa nowadays would choose to isolate themselves in Orleans. Train or not, it will be a horrible commute to Kanata, or to Gatineau if you wind up there in subsequent postings. Orleans to downtown is a half hour, often longer on the way home, and Orleans is pure suburbia, which you may or may not like. Kemtpville too, is way too far for most peoples' tolerances, unless you are obsessed with small towns and like hyper early mornings. You get a 45 minute drive to the edge of the city then could have another half hour on some days to get downtown.
I would recommend you suck up a smaller home. It's not realistic to expect to have the same size of home in a large city like Ottawa as you could get in the smaller communities around most CFB. If you can accept a smaller footprint in favour of a better location your options open up. Your circumstances will drive that, of course. If you have 4 kids, you need space lol.
Nepean is quite central and has a mix of large, new homes and older homes too. Barrhaven is new, affordable and quite central, offering all (or more) of the suburban amenities of Orleans, but from a much better (more central) location for DND staffers. Gloucester is as far east as I would recommend. Lots of folk do the Quebec side too, Aylmer is small and charming, and Chelsea is not too far a drive although bridge traffic from Chelsea is brutal in the morning. If Quebec is your thing, I'd avoid Gatineau proper, the Eastern part of the city, as the congestion and choke points are not workable. Kanata and Stittsville are great for Carling access, but far for downtown or Startop or Gatineau, although lots of people still live out there and suck up the commute, which can be 45 minutes to an hour each way to most places other than Carling or Tunney's.
Unless you are a fan of early mornings and long commutes to work in the dark, both ways, all the time, day after day, month after month, year after year, buy as central as you can afford, would be my advice. The commute in Ottawa is unlike anywhere else we get posted, and it can really change your QOL, depending on your circumstances and lifestyle.
Good luck / bonne chance!