A number of people I’ve spoken with are curious about the process used in selecting bishops in the Latin Church. While I can’t say I have first hand experience of the procedure (except for being on the receiving end), there are a few details I do know, particularly as it concerns auxiliaries.
When a diocesan bishop believes it would be pastorally advantageous to have one or more auxiliary bishops appointed for his diocese, he submits a list of candidates to the Holy See (i.e. the Vatican) through the Pope’s diplomatic representative in Canada (known as the Apostolic Nuncio, i.e. a kind of ambassador). This list must have at least three names; this is why the list is called a terna (meaning “three”). I imagine the bishop making the request can list them in an order of preference, although canon law itself is silent on that issue.
Once the terna has been submitted it must be vetted to make sure each candidate means the minimum criteria and is at least credible as a possible candidate. The minimum criteria include age (at least 35 years old), experience (at least 5 years of priesthood), education (at least a licentiate in Biblical studies, theology or canon law), and other human factors like a good reputation, solid faith, good morals, piety, pastoral zeal, wisdom, prudence, and so on. These criteria are listed in the Code of Canon Law, canon 378.
From what I hear, it is possible for a terna to be rejected outright! This does not mean that none of the candidates are worthy, but my understanding is that all three candidates must be true potentials, so that the Pope has a genuine choice. One would not want to have a situation, for example, where a diocesan bishop, hoping for one name in particular, was tempted to put down two others whom he knew were unlikely to be chosen (in other words, trying to rig the outcome).
Once the list of candidates has been initially vetted, a process of inquiry begins, led by the Apostolic Nuncio. He writes in secret to priests and lay people who know the candidate(s) and asks them to write back with responses to a detailed set of questions. I should point out that the candidate himself is not asked any questions, nor is he asked about the other candidates. This process is meant to hopefully avoid politics and “campaigning for the job”, and to the extent that secrecy is maintained a potential candidate could truly be left in the dark. For example, I imagine that at least a few of the 20 priests I live with here at the cathedral were consulted regarding me, and yet — hats off to them — none ever let on.
One never knows what the inquiry process might turn up, but assuming the terna remains valid (i.e. the three candidates remain credible), the reports are sent to Rome to the Congregation for Bishops (or, for mission territories, the Congregation for the Evangelization of Peoples). A committee composed of bishops and cardinals examines the reports, checking to make sure that proper procedure was followed, and that the candidates truly are potentially suitable. Ultimately, the Cardinal Prefect of the Congregation for Bishops then presents the list to the Pope (I imagine with a recommendation, although I can’t confirm that), and the Pope makes the final selection.
There are some who believe that the general procedure for the selection of bishops should be more open, more democratic. I suppose the matter could be open for discussion: after all, the Eastern Catholic Churches have different methods in picking their bishops, and even the Latin Church has exceptions to its general process (such as in Switzerland). Heck, in the Acts of the Apostles (chapter 1, verses 15-26) we see that Saint Peter, while he led the process to pick the successor to Judas, left it up to the community to suggest names — with the final choice left to the equivalent (in those days) of flipping a coin! The current process does have one major advantage, however: it prevents undue influence from civil authorities. History — including very recent history — is full of examples of kings and governments trying to influence (or even force) the selection of particular candidates for bishop, often with unhappy results. Regardless if we were to tweak the current process, or even change it completely, I would definitely want to continue to see some mechanism for insulating the choice of successors to the apostles from undue outside pressure. It is all about freedom, including the freedom of the Church to pick her own leaders and ministers according to the standards of her Tradition.