modalInstanceを生成する際に下記のようにする。

var indexController = function($modal) {
    var that = this;
    
    this.data = {};
    
    this.open = function() {

        var modalInstance = $modal.open({
            templateUrl: 'confirm.html',
            controller: 'confirmController as confirmController',
            resolve: {
                data: function() {
                    return that.data;
                }
            }
        });

        modalInstance.result.then(function(rtValue) {
            // ok function
        }, function() {
            // dismiss function
        });
    };
    
}

var confirmController = function($modalInstance, data) {
    var that = this;
    
    this.data = data;
    
    this.ok = function() {

    };

    this.cancel = function() {

    };
};

    
angular
    .module('controllers')
    .controller('indexController', ['$modal', indexController])
    .controller('confirmController', ['$modalInstance', 'data', confirmController])
;

的な感じ。