There have been experiments with using HSB to control crappie, and it did work. The issue is, HSB have much smaller mouths than LMB, and the size of crappie they can eat is limited. I'd probably recommend GSH, but since you already have predators established, it will be hard to get them to take root before becoming tasty snacks.
White Crappie are better suited for muddier ponds or ponds with persistent plankton blooms.
Black Crappie do better in clearer ponds with visibility greater than 3'.
But, like you mentioned, Crappie are very irregular spawners. You might get nothing or very little one year, and the next year you can't throw a stick without hitting one. Just something to think about. I don't think Crappie would be the ideal forage fish dedicated to feeding your HSB. Shiners (and pellets) are the best way to go, imo, since you're too far north for Shad.
