It's my understanding that St. Clair is a fairy shallow lake so any breakline you can find should produce. In the end of May you will probably encounter, pre, post and spawning fish. From what I've read and heard about the lake, tubes are hard to beat, soft jerkbaits, and topwater, spinnerbaits, are good choies.
I've also read that certain ares of what are called pencil reeds can be good.
Good luck!