It can’t be helped - differences?

So I have heard:

- 仕方がない
- しょうがない
- 仕方あるまい

And the translation I've seen for all 3 is: ''It can't be helped.'' Is there a particular difference among the 3?

Edit: Secondary question. Why isn't 仕方あるまい, 仕方があるまい?

Yes, they all mean "It can't be helped."

The third one can be 仕方があるまい as well. THat one is a bit old-fashioned wording, thus can sound a bit dramatic, thus the sense of resignation ("I've given up!") is a tad stronger, IMHO :)

Is there any difference between the sentences (nuances)? What is the difference between 仕方 and しょう?

仕方がない and しょうがない are identical even in tone/nuance. The latter comes from 仕様（しよう）がない, so they say the same "no way/method to deal with it" = can't be helped.

しかた（が）あるまい is, as I said, a bit old-fashioned way, it sounds a bit exaggerated or dramatic, "Weeeell, I guess it cannot be helped, I must say" kind of definitive, authoritative tone. I (a Japanese woman my 40s) would not use it :)

Thanks AK!

Is there any difference between the sentences (nuances)?

" 仕方 (が) ない " or " しょうがない " does not include a word to imply a speaker's attitude of mind, while " 仕方あるまい " does.
Here " まい " is an auxiliary verb to imply that the speaker believes "S would never."
So, " 仕方あるまい " can sound offensive or cynical if used for another person's situation.
e.g.
- 人前［ひとまえ］であんな失礼なことを言ったのだから、彼は批判されても仕方あるまい。
(Having been rude to say such a thing in public, he must have no way but to accept criticism.)
You can soften the tone by using " 仕方 (が) ない " or " しょうがない " instead, with a verb like " 思う " and a particle " よ " .
- 彼は批判されてもしょうがないと思うよ。
(I suppose he has no way but to accept criticism.)