Here's the thing about "cancelling" the election. Elections are run by each state independently. The Constitution only specifies that each state will send electors. To cancel the election they would need to disrupt the process in enough states to prevent Trump from getting to 270, in which case the 12th amendment is automatically invoked.

In this scenario, the House elects the president after they are sworn in on Jan 3. There would still need to be those down ballot races to determine the incoming Congress. I highly doubt that any order from the federal level to cancel elections nationwide would be followed. They would have to pull some major shenanigans to keep people away from the polls.