I'll be glad to tell you how the process worked when I was named.
A search committee was established, and I believe it has always been chaired by the president of the Canadian Institute of Chartered Accountants. I'm not sure who else was on that search committee, but they contacted the major accounting firms and various professional organizations to bring forward names of people who might qualify for the position. An ad was placed in the newspaper for people who wanted to apply. Then there was a selection committee, chaired by the President of the Treasury Board, who then conducted interviews of a short list of probably five candidates. Then that committee made a recommendation to the Prime Minister. In my case, it was an appointment by the Prime Minister. I understand there was also some consultation with the chair of the public accounts committee at the time.
That process will have to be modified now because of the Federal Accountability Act, which requires some involvement of the parliamentary committee. I don't think it's an actual approval, but there is some hearing before a committee--I presume it's this committee--on the candidate who is being proposed.