I bend over backwards to try to accomodate their scheduling needs. Especially since most of them are in my choir as well, I try to avoid at all costs scheduling them for cantoring on the same weekend the choir sings. Sometimes it's unavoidable, and they understand, but I've always found that a happy cantor is a loyal cantor.

Before I came, they were on a "sign-up" basis. This was a disaster which left many holes that the organist/DM covered himself. Since I don't sing, I laid out the expectation right away that there should be a cantor at every Mass that the choir (or some other ensemble) doesn't sing, and I put them on a schedule. Some questioned this but they've all adapted and thrived on it, and I haven't lost a single one of them. In fact, we've added at least 4 cantors (and brought back a few others who had lapsed under my predecessor), and are now at a place where there is always coverage. Every once in a while there will be a slip up where someone doesn't show, and I always follow up with them. They are all of varying degrees of ability: I have vocal and opera performance grad and undergrad students from the private university across the street, and I have people who have no vocal training whatsoever.

I made a pitch to the congregation my first weekend here: got 2 cantors and 3 choir members out of it, all of whom I'm glad to say have stuck with it and it been nearly 2 years. So that does work somewhat. I would also just say that networking is important, as is attending Mass in the pews when possible to find out who sings, and then invite them to audition for you. Personal calls go a long way! Bulletin announcements, on the other hand....forget it!

As much as possible, standardise the music program across the masses on a given weekend.

Where I sing, the cantored masses usually don't have chanted propers, but use suitable hymns instead. It works well because the cantored masses are usually much smaller than the choir masses, so at the choir mass there is time to chant the full communion psalm AND sing a communion hymn, whereas at a cantored mass, the hymn is usually sufficient.

Standardising the music across a weekend means that different cantors don't feel that they've been given unfairly difficult music.

Also, consider the voice ranges of your cantors. It may work out better to play music up a tone for Tenors and Sopranos from the usual pitch of the music. It may also be worth considering the voice range of the hymns you use. Modern hymns tend to use a rather unnecessarily wide pitch range. I prefer stuff that has a range of not more than 1 octave.