"Can we get this over with?"

Solution 1:

1. There is no problem with this phrase - it is idiomatic English.

2. With is part of the compound adjective over with. To be over with means to be finished. As far as I know, it's only ever used with the verb be.

3. It's fine as it is. You could say "Can we get this finished?".

Solution 2:

Well, if you really want to, you can rewrite it as:

Over with can we get this?

but you end up sounding like you're chanelling Yoda.

So thank you for providing an excellent refutation of the "never end a sentence with a preposition" rule. Next time somebody tries to tell me how to speak English, I'll take a deep breath and say, "Okay. Over with let us get this..." :-)