If you’re currently paying for it, you won’t get a free trial. Personally, I tried Apple TV almost a year ago, and when I re-subbed for the trial I got a month of it free. Your mileage may vary.
You won’t pay for Apple TV or Apple Music after they expire. Once you start paying for AppleOne, you will gain access to everything.
So my recommendation, if you care about Apple TV or Apple Music, you should not stop the subscription till you are paying for Apple One; or the other way is to skip AppleOne trial and start paying right away.