Both wrong. In this scenario, no cash is borrowed. The 1M cash perfectly pays for the 1M of longs. Only longs can create cash borrows, when you are long more than your cash.
Shorts create stock borrows instead. You pay short interest based on the stock borrow/lend market, but you actually can receive interest from the cash proceeds if the fed funds rate is positive, and depending on your broker.
Gross exposure does not need to be covered by cash. Mechanically, shorting does not require cash, and it is only constrained by regulations and/or broker risk limits (reg T, PM, house requirements).