we are trying to move the sidebar (opc-sidebar) to the top of the page via xml update but can not find the right xml file and code to do so. Can someone point out to us how to do this?
I'm sorry but I can't really help you with this issue, I'm running into some of the same as you are. Let me guess: You need to make the adjustments for the German "Buttonlösung"?
I first tried moving the "Place Order" button to the sidebar and stumbled over this: http://magento.stackexchange.com/questions/155010/magento-2-move-place-order-button-from-payment-to-...
But the suggestions there just move the aggreements so I edited the answer and provided some code from my research.
After thinking and trying around I thought it would be too much to but each and every payment methods "Place Order" button in an own knockout.js template etc. and then move and update the button in the sidebar when a different payment method is selected.
So I thought about moving the sidebar right into the payments-list or any other fitting area so the totals will be displayed right before the "Place Order" button but I can't get it working.
Okay, I'll get to it: Since it's been a while, maybe you have already found a solution or an approach, would you share it with the community?