I will suggest four scenarios where different types of people would be desirable as candidates.

First, there's "whoever's rich and willing". Under this scenario, the business offers WBE to the highest bidder, presumably with the promise of immortality (and perhaps fame/notoriety: hey, the first human to be emulated!) as enticement. This would seem to presuppose that the company has managed to persuade the rest of the world that the emulation definitely will work as advertised, in spite of its hitherto lack of human testing. And/or it's a non-destructive procedure.

Second, there's the "whoever's craziest" scenario. Supposing it's a destructive process and--ex hypothesi--as yet untested on humans, the company might struggle to find anyone willing to undergo the procedure at all. In this case, I would expect mainly enthusiastic volunteers from LW who have followed the technology closely, possibly with a smattering of individuals diagnosed with terminal diseases (see also next scenario).

Third, there's the "humanitarian" (or, if you're cynical, the "cook up some good P.R.") scenario. Here, the company selects someone who is either (1) in need or (2) likely to contribute to humanity's betterment. Good candidates might be a sympathy-garnering, photogenic child with an incurable disease, or an individual like Stephen Hawking, who has clearly proven to be a valuable scientific asset and is a well-known public figure--yet who is in the late stages of ALS.

Fourth and last, there's the "ideal worker" or "capitalism at its finest" scenario, inspired by Robin Hanson: here, the company might choose someone specifically because they anticipate that this individual will be a successful worker in a digital environment. Aside from the usual qualifications (punctual, dedicated, loyal, etc.), some extra pluses here would be someone with no existential compunctions about being switched on and off or about being split into temporary copies which would later be terminated after fulfilling their roles.