Since you are using an admin route the user would have to be log in as an admin user before they could view the order.
However you could use the existing code as a template and create a frontendfrontend
d route and copy the necessary code as needed.
For security purpose you may want to add a token to your email url for security (e.g md5 of the protect_codeprotect_code
in sales_flat_ordersales_flat_order
)