First, you can use external CAN modules that speak SPI/UART/I2C, making it easier for you.

Second, you will still need an additional CAN driver to work with the voltages required.

Check out Microchip's offerings for 1 & 2 at https://www.microchip.com/design-centers/can
At the bottom of the page is a Documentation tab with Application Notes available.

Third, depending on the application you are wanting to apply CAN to, you may have to learn the protocol. Automotive CAN protocol is spelled out quite explicitly in SAE J1939, J1979, J2178-1_2, and the all encompassing J1699 (just mentioning the few I have). Other industries operate under various other protocols. If you want to communicate with a CAN product that is not governed by any protocol standards, GOOD LUCK!!

CAN is not an quick learn like UART or SPI. You must REALLY need to use it or you'll give up before you conquer it.