Kansas City MO proper does not have any prohibitions against Open Carry. Some of the suburbs do, such as North Kansas City and Parkville. I don't know about the Kansas side. If you can tell us more about where you will be, I can provide more detail.
The political structure of St Louis is unlike anywhere else in the world. You move between different little cities all over the place, even when your in St Louis county proper which is different from St. Louis City. I just CC in St Louis, because I don't have the mental capacity to know where OC is legal and where it isn't.
You might get hassled a bit, but it's not too bad. Most of the KCMO PD is up to speed on open carry. There are exceptions though.
Missouri has different laws that apply to people with and without a CC license. If you have a CC license, you can go most anywhere except federal property. If you get asked to leave, do so and there is no problem. If you don't have a CC license, do not go into prohibited areas, or you will likely not like what happens.