From my perspective; I'd look at is the land easy to acquire and could accommodate the stadium, an expansion, parking and bus facilities.
Because of the fact that Moncton got the CFL game and it looks like more things could happen - for the sake of expendiency, my thought was mainly a suburban location because you could take raw land and just build it and get it done.
That being said, if Moncton hadn't been so successful in getting the CFL and we had time then I'd want to go through a full review of many sites in HRM (including CFB Windsor) to see about acquiring the land; because if the time was available (not a rush issue); then you could do a whole grand redevelopment scheme for an area and have the stadium for a major piece. I don't think that's necessairily an option at this point?
Shannon would be a spot where a redevelopment scheme could be done that incorporated the stadium as a major component, the transportation issues could be resolved with that scheme.
However, if we are trying to take advantage of public reaction to Moncton's success, then I'm guessing greenfield would be where it would go, simply to make the selection process simple and the development time less (since you wouldn't have to do any reclamation or all the work you would do with brownfield sites).
Btw, I did some scaling of distances and the only place that would end up being equi-distant to everything would be in the middle of the harbour. So i'm all for a new man-made island in the middle of the basin.