Robust CAN communication requires "clock accuracy less than or equal to 0.5%". Period. There is no requirement that this come from a crystal oscillator (how would it even know?)
It's easy to achieve better than 0.5% accuracy with a crystal, which is why use of a crystal is recommended. However if you can provide 0.5% or better accuracy in some other way then that's fine.
Thanks for your feedback. Do you know if the internal oscillator of the PSoc 5LP (CY8C5888AXI-LP096) is capable of this level of accuracy?
Nope, unless you are using USB mode and locking to the USB bus (not familiar - suppose it uses a frequency reference? You would have to have a continuous USB connection).
From Document Number: 001-84932 Rev. *L, table 11-80 which describes the IMO (Internal Main Oscillator):
Looks like the accuracy range is +/-7%, best is -1%..+1% at 3MHz and the 0C to 70C temp range, UNLESS you use 24MHz - USB mode, with oscillator locking to USB bus (I suppose the USB bus provides an external frequency reference).