God I despair, why put yourself through this!
Don't you have a Small Claims Court? Or something similar. If my camera was in warranty, if the first repair failed, I would simply inform them to replace the entire camera - as you have quite reasonably given them the opportunity to fix it , and they failed!
In the UK, in such a scenario, the Courts invariably will side with the customer - and Canon know this. They would capitulate, why....?
1. They dont want the extra expense
2. They dont want the bad publicity
3. They want to continue their "unfriendly customer attitude" - publicly exposing the fact, that a customer will easily win, means they will have to do the right thing for everybody. They will prefer to bury it.
If all customers took this attitude - Canon would change!
Sorry but grow some b@@@s and stand up for yourself.
They will cave as soon as the writ hits the desk, if not before.