Thinking of exchanging 60d for a 57

I suggest you look into professional based reviews. I used to own canon 50D and among all Canon semi-pro cameras I've read about including the 7D and 60D, 50D got better ratings overall. Though I wouldn't say I am really satisfied because I still review my picture files and still end up choosing pictures taken with my sony A100. Sold my 50D recently and chose to go sony all the way now. got a slt55 and 57. Keeps me satisfied. 

Hi i Just Bought the Sony A57 and i would say i am pretty impressed with it.if you like to have more burst rate go for the A57 as it has 10fps and 12fps in Crop mode which would be 8MP.i haven't compared the image quality though, But the A57 produces some amazing results in low light.it does have a fast AF.and Continuous AF in Movie Mode.i would suggest you to have a hands on both the camera in-store take your time with it.All the Best. 

For fast moving objects the Canon will be a better bet.  It will focus faster (given you have a proper lens) and have faster shutter speed at a given ISO.  The Sony has a higher frame rate due to its semi-transparent mirror.  Yes, you get more frames per second but loose about 1/3 of a stop in doing so.  When Canon first released the EF lens it was the fastes focusing and most accurate system.  Nikon has since leveled the playing field.  Most people wouldn't be able to tell the difference between photos taken from any of these cameras.  So, unless you are getting paid to use a perticular brand then stick with what you have.