I think it's great that you get a choice! When I did my student teaching I was assigned someone I'd never met at a school I'd never visited; the university automatically made assignments without student input.
In the classroom, I've had several student teachers. I would get a call from a university supervisor requesting a placement in my room, and if I agreed, a few weeks later I'd get a call from who ever they assigned to my room. I never knew ahead of time who it would be.
Is this now a common way to place student teachers?