Upload & Sell: Off
Generally, Canon will have bodies that they consider to be "golden samples" where they know every attribute is spot on and they'll use those bodies to calibrate lenses to where they meet spec (as it relates to that golden sample body.)
If you truly want YOUR glass to work perfectly with YOUR body, then you really should send both. HOWEVER, if you have more than one body, that's not necessarily going to work very well.
For the record, everything I've ever posted here has come from a mix of three bodies and nine lenses and none of them have ever been to Canon nor have I ever done any micro-focus adjustments to anything. I do need to send my 24-70 to Canon for some TLC because it got dropped, but so far, it's still working well insofar as I can tell. There is cosmetic rash and the front ring is slightly out of round, but otherwise it still makes good images.