The correct option is
B wouldn't we
The question tag converts a statement into a question. The tag is formed using the auxiliary verb and the subject from the statement.
Also, the question tag is in the negative, when the statement is positive, and vice versa.
In the given sentence, the modal auxiliary verb is 'would' and the subject is 'we'. Since the statement is positive, the question tag will be negative.
The tag hence formed is 'wouldn't we?'.
Hence option B is correct.
Option A: This option is incorrect because 'do' isn't present in the statement,
Options C and D: 'Haven't we' and 'hadn't we' are both incorrect because the verb 'have to' in the sentence is the main verb. Generally, question tags are not formed with the main verb, but the auxiliary verb (would).