3+ month delay in reviewing the revision of paper, what can we do?
Aug 15 to at least Dec 2 seems like a very long period for a decision based on a minor revision. Particularly since the procedure earlier seems to be very timely. Sending an e-mail to the handling editor seems in perfect order. There may of course be some natural reason for the delay but after more than three months you should certainly enquire.

As for the content of your request just make is short, to the point and polite. Do not assume anything or be unfairly judgemental, you do not, yet, know the reasons for the delay. If you have some "excuse" for why you are extra anxious to get a response, please mention it. This could be that you need to show your updated publication list for applications or for some other official reason. This will of course not mean you receive special treatment but will make the editor aware of the delay and the possible effects it may have. But, a short e-mail will suffice.