I just got Cakewalk Sonar and would like to load some existing mixes to play with. 
 
Anyone got a link or something?
 
Thanks

Just Google "remix contest".

http://forum.cakewalk.com...Practice-m3537464.aspx
 
http://www.cambridge-mt.com/rs-bkg.htm
 

fwrend has pointed you to the cambridge-mt backing stems which is not the same as the multitrack sessions.
 
The multitrack sessions (which are the best resources) are normally here:
 
http://www.cambridge-mt.com/ms-mtk.htm
 
But as you will see this site is temporarily down but he is moving the multitrack sessions to a new server. Check back after a week or so and you should be good to go.
 
There are literally hundreds of great multitrack sessions to choose from. 
 
Forget remix contests as well. You will have to join up and go through the hassle of getting them. Plus the tracks often have effects and things burned in. Not as good as a raw multitrack.

Here's a good resource:
 
http://behindthespeakers.com/300-free-multitracks