The above sentence has nearly 10 million Google results. I've seen it used in books, television shows, and in casual conversation.
But what if I want to replace the word "can't" with "shouldn't"? How would I phrase the second half of the sentence then? "We shouldn't do that, now should we?" seems like the obvious choice, but based on a Google search, it doesn't seem to be very common. Is there a more common way of wording that sentence?