To interface a Simulink model with a NI CAN board, you can use LabVIEW and the Simulation interface toolkit.
You will find below a link to our web site which explains how this works.
http://zone.ni.com/devzone/conceptd.nsf/webmain/9F81C2072EE1F52686256DB0006769EA?opendocument
I hope this will help you.