The default behavior of a Cisco client device is that it connects to the AP that has best signal strength available. But you can limit the clients that can connect to any particular AP through MAC authentication. You need to provide the MAC address of the client to the AP so that the AP can allow only those clients and restrict all the other clients that are not part of the allowed MAC address list from connecting to that particular AP.

For MAC filtering there is a limit of 43 using the GUI and 2000 for the CLI and if we use a Local RADIUS server we can add up to 50 users.