Pass CF7 form data to plugin

A complete answer would be a little complicated since ‘plugin A’ and ‘plugin B’ should be analized in-depth so check for available hooks and filters, but if I understand you wrote your own plugin so you have full control on it.
That said, a starting point to get submitted data from CF7 is the following:

add_action("wpcf7_submit", "Stack_308450_forward_cf7", 10, 2);

function Stack_308450_forward_cf7($form, $result) {
    // var_dump($submission->status);
    $submission = WPCF7_Submission::get_instance();
    if ($result["status"] == "mail_sent") {
        $posted_data = $submission->get_posted_data();
        Stack_308450_wpcf7_posted_data($posted_data);
    }
};
function Stack_308450_wpcf7_posted_data($posted_data){
    //do something here
}

I’ve personally implemented some functions on CF7 submission: in this case we’re processing data after mail sent so you should indagate yourself if you find a more appropriate hook such as “wpcf7_before_send_mail”:

function action_wpcf7_before_send_mail( $contact_form ) { 
  // var_dump($contact_form);
};

add_action( 'wpcf7_before_send_mail', 'action_wpcf7_before_send_mail', 10, 1 ); 

Consider also issue regarding validation on submission which are also involved in this process.

Here follows a
List of available CF7 hooks»