You might think I have a lot to say about this. (A top UK newspaper just emailed asking me to write something.) I don't.
I have very little to say. And what I do have to say is fairly obvious.
I think Britain needs him more than Canada does, because the British economy is in worse shape than the Canadian economy. (I was touching wood as I wrote that, because, for example, Canadian house prices have been falling a little recently and I can't be certain that they won't fall a lot.) And the Bank of England is more involved in supervising financial intermediaries than is the Bank of Canada, and that would probably be Mark Carney's comparative advantage.
I can think of two good candidates (I'm not going to say who) to replace him as Governor at the Bank of Canada. There are almost certainly many other good candidates whom I know nothing about. I hadn't heard of Mark Carney before he became Governor.
Some people are very good at networking and knowing who's who. I'm not one of those people. My guess is that almost all journalists are very good at networking, and that most economists are bad at networking. The reason we became economists in the first place was probably because we were no good at remembering lots of people and their names, so we didn't do very well in history or literature.