I've answered your questions below.
Possibility of Unlocking pins:
There's only one restriction for SPI chip select pin. You can select any pin that is exposed on Arduino header to act as SPI Chip select. The only restriction being - it should not be SPI pin(SPI Clock, SPI MISO, or SPI MOSI).
Currently, we don't support pins that are not exposed on Arduino header. If you intend to use those pins, please let us know. We can consider adding support for them in future releases.
Interrupt Pin: This pin needs to be a pin that has interrupt capability. On AVR targets, these pins are limited but for Arm targets, there are plenty of options to choose from.
Support for more than one CAN channel:
Since the communication with the CAN chip is happening over SPI, there are some limitations when it comes to communicating with multiple CAN chip over SPI. We'll consider this for future releases though.
Thanks a lot for your feedback.