I have since broken out my version of the canbus library to its own github repo. Here it is: git://github.com/collin80/due_can.git
It is renamed so as to not conflict with the official Arduino Canbus library. Make no mistake, mine is not official, just the one I use. It's more object oriented and, I think, easier to use. But, it's your choice. There is an officially sanctioned library but you have to check out the can branch of the Arduino IDE on github (the whole thing).
But, and this is a big but, you probably have to download the official canbus library branch anyway. There are changes to some of the libsam files that are necessary for both canbus libraries to properly compile. I suppose I really should figure out what those changes are and import them into my library so that stock 1.5.2 will work. I'll try to do that within a few days. So, it might be best to wait a few days.