Enforcing canonical URLs with multiple custom post types

I tackled subordinate post types with a similar vein but was not as strict on the canonical url aspect; however, I ran into a similar situation with deeplinking custom WooCommerce product type links.

I leveraged the template_redirect hook to push a 404 if it didn’t match the route and the post_type_link to ensure the meta tag for canonical link and all the_permalink() and get_permalink() references matched the intended link.

A snippit of the way I would recommend handling this:

add_action( 'template_redirect', 'wp20140320_template_redirect' );
public function wp20140320_template_redirect(){
    global $wp_query, $post;

    // the character post type has the book id set as meta?
    // or could set as post_parent if you don't have characters heirarchical
    $book_id = get_post_meta( $post->ID, '_book_id', true );

    // compare_parent_slug_to_id to check required $book_id against set parent book slug
    if( $post->post_type == 'character' && ! compare_parent_slug_to_id( $book_id ) ){

        // set is_404 since post type is character and parent slug does not match set
        $wp_query->is_404 = true;
        status_header(404);
        include get_404_template();
        exit; // maybe a better way to gracefully exit?

    }
}

Modified from source