MACsec is the established link-layer security for automotive Ethernet, while CAN and CAN FD — still carrying most safety-critical traffic — lack an equivalent. We address this gap by reusing MACsec for CANsec, the Layer 2 security protocol for CAN XL (CiA 613-2), and extending it to CAN FD via the CAN FD Adaptation Layer (FDAL), bringing a consistent trust foundation to existing nodes. Scapy supported this work end-to-end: integrating CAN XL from the Linux kernel, implementing CANsec and FDAL, generating test vectors for vendors, and enabling a proof-of-concept Ethernet application over secured CAN FD.