I have never used the XM radio app on my BlackBerry but I hear it is pretty good. The app and service was previously only available in the US but XM has now extended it across the border to Canada. The app lets you listen to XM online+ over your 3G or Wi-Fi connection with over 100 channels of music, talk, sports, & news.
There is a 14 day free trial for new users after which it is $7.99/month or if you already subscribe to XM you can get the mobile app subscription for $2.99/month extra.
Check out the details at xmradio.ca/blackberry