I quite enjoy the concept of the iTunes Radio and have been frustrated with the lack of availability of the service in Canada. To my surprise, it is very easy to unlock the radio. So I present you the instructions so that you may enjoy it as well.
First off you will need a US iTunes account. Not to worry, this instructional will provide the information needed to create it.
Once your US iTunes Account is set up, simply use it as your log in on your Apple device. Below are quick instructions for specific devices.
Navigate: Settings>iTunes & App Store. Here log out of the current account and use your US Apple ID. Open the Music app, there will now be a Radio icon at the bottom. Enjoy your new listening experience.
Navigate: Settings>Apple IDs>Add account. Use you newly created US Apple ID. Returning to the home screen you will notice a few new icons including the iTunes Radio icon on the top row. Enjoy.
Open iTunes and navigate to the iTunes Store with the button in the upper-right. Log out of the current account and log in with your US Apple ID. Navigating to "Music" with the drop-down menu in the upper-left will provide a "Radio" option in the picker menu at the top of the screen next to "Songs".
Because you are logging into a different Apple ID you will not have access to your cloud based media content. Also, if you want to purchase any content from the various Apple media Stores you will need to log back into your usual Apple ID.