I think they are largely interchangeable. I actually think “open government” has been the more popular term from other governments, and I think part of it just comes down to marketing, quite frankly. Some governments have seen the marketing value in being portrayed as open and have latched on to the “open government” term, but the reality is that people in the area who are talking about what governments could and should be doing are largely talking about the same thing, whether they're talking about open government or open data.
From my perspective in Canada, I don't care what we call it, but we need to recognize that there's a certain amount of urgency here, when we contrast the pace at which we've been making change on some of these issues here in Canada with the pace of some of these other jurisdictions. Whether we call it open government or open data, we need to get on with the job.