To the best on my knowledge the CAN support in STM32CubeProgrammer is via the STLINK/V3SET boards. The API also has examples.
For the CAN protocol implementation use the following app note, and code a solution for your PC side CAN implementation/drivers
https://www.st.com/resource/en/application_note/cd00264321-can-protocol-used-in-the-stm32-bootloader-stmicroelectronics.pdf
The support costs for third-party CAN implementations is likely too high, and if you have specific hardware/software you're familiar with, implementing the protocol should be straight-forward enough.
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