Hi from Ottawa. If you are moving back here for a job, why wouldn't you move closer to work? Also note the new light rail system is under construction, so that could also factor into where you might live wrt where you work. Long commutes may be standard in other places, but unless you want to live in the burbs for family reasons and then have a commute to work, I'd advise against that in Ottawa (or anywhere!).

I've not lived in London, but grew up in Montreal and lived in Toronto. I've been fortunate enough to visit many US and European metropolitan areas. In saying all that, I really find Ottawa to be a nice-sized small city. It's a government town for sure, but there is also a lot of Aero & Defence (where I ended up) as well as high tech (Shopify, Apple, Amazon, QNX/Ford's new self driving car centre). It's big enough to have pro sports teams, but small enough that you can be in the country in 20 minutes if you want to. No 16 lanes of highway anywhere in sight, either.

At the end of the day though, try not to worry about it too much. As others have said in this thread, the first job will define a path in life, but so will the second job, or that next person you talk to on the bus, it's all a big random walk. You are fortunate to have two interesting opportunities in front of you, so have fun and good luck.