The cannon river down towards cannon falls / Randolph has a ton of carp and channels. I’ve found using chicken liver wrapped in cheese cloth or thule fabric is a good way to eliminate the sheepies and focus on the cats and also keep the nasty stuff on the hook. As far as flatheads go…. I’m still searching myself. The cannon hasn’t produced flatheads for me at all. I’ve never heard of them there, but that doesn’t mean they aren’t around. Carp seem to be in every waterway so just try a bigger river with worms.
I’ve heard a lot of guys find trout on the vermillion, but I’m not a trout guy so I have nothing. Good luck!