You can try it. The transceiver is really fairly invisible to the way the library works. There is just a small amount of code to support an SN65HVD234. What happens is that the enable pin is set to enabled and the RS pin is controlled to manipulate the slope rate. But, you can easily make a board that does its own enabling and slope control and just not hook that stuff up to the Due at all. So, that brings me to whether you can use your transceiver. I suppose you could. It would probably accept the CANTX signal from the Due just fine. Then, as you said, you have to use a voltage divider or buffer chip to turn the 5V CANRX signal from the transceiver into a 3.3V signal to the Due. Chances are it would accept 2.5v. It isn't ideal but if you're just making something for yourself it makes sense to use whatever you happen to have on the bench.