I've written a while ago about the Ticats probably hosting the 2016 Grey Cup. Amusingly that post gets a lot of views. Tim Horton's Field will be completely ready one assumes and Winnipeg will have hosted the 2015 Grey Cup in their new stadium.
I looked and apparently the announcement that the Bombers were going to be hosting the 2015 event was made this year around March 26th. So likely at the end of March next year, we'll hopefully get confirmation and the team and city can start planning.
One issue is how many seats the Ticats can add in the end zones for the Grey Cup to get above 24,000 seats. The Ticats do have a lot of box seating, which I'm assuming would be priced expensively for the Grey Cup.
The last time the Cats hosted was 1996, which while a great game, wasn't exactly a great financial success (the previous Grey Cup before that was in 1972). I think it is fair to say that Hamilton is doing better than in 1996 (with way more downtown hotel space) and with Bob Young and his Ticat organization leading the preparations, a 2016 Grey Cup would stand a much better chance of success.
Ottawa is obviously an option, but I see them more likely to host the 2017 Grey Cup. Likely their team would be better by then and have a better chance to be in the Cup.