The clue to uncancel an order, is that - while you can change the order itself by changing its state and status, you also need to uncancel the order-items within that order. The following PHP-script could be run from the command-line to uncancel a specific order.

<?php
require_once 'app/Mage.php';
Mage::app();

$order = Mage::getModel('sales/order')->load(1382);
$order->setState(Mage_Sales_Model_Order::STATE_COMPLETE);
$order->setStatus(Mage_Sales_Model_Order::STATE_COMPLETE);
$order->save();

foreach ($order->getAllItems() as $item) {
    $item->setQtyCanceled(0);
    $item->save();
}