とあれば

とあれば means "if it's a matter of…": the condition is weighty enough that the speaker will do something they otherwise wouldn't, or that the result follows as a matter of course. A noun or a な-adjective takes it directly, with no だ; a verb or an い-adjective is in the plain form.

The second half is often a show of resolve: なん何でもする, くろう苦労もいとわない厭わない, ことわる断るわけにはいかない.

とあれば or なら

なら is the neutral "if" and fits any condition. とあれば puts weight on the condition: it is the reason the speaker goes out of their way, or the reason the outcome is obvious. For an ordinary "if", use なら.

とあれば belongs to writing and formal speech. Set phrases such as ひつよう必要とあれば and おのぞみ望みとあれば turn up in polite conversation too.