Even CIC isn't THAT cruel. Can you imagine how scary it would be to forward it without having a peek inside the envelope?!?! What if the FBI IHSR letter is WRONG?!?! :-\
Yes, you can (and should) open it...exhale...then forward it (with or without the envelope) to CIC, if not including it with your application.
I still find it shocking that there are absolutely no security features on the FBI paper; no raised seal, not on tamper-proof paper, nothing.