Google doesn’t let you download Chromecast app in Canada yet as the Chromecast is not available here. Here’s a hack install the Chromecast app on your Android device:
Download the app file below
Move the file to your Android device (easiest way is by putting it on Dropbox)
Open the file from your device ( You will have to change the security setting to allow your device to install files from sources other than Google Play.
If you want to play your music with the chromecast, you can do so using the Dropbox DropTun.es webapp, it’s very easy. Just connect to your dropbox account, select the song and Chromecast from your browser.