としたら

A sentence + とする can be used to present a situation translated roughly as "Suppose that..." So if we take a sentence + としたら (which is する in its "if" form), it translates as "If we suppose that..." It can be used for presenting hypothetical scenarios. To make it even clearer that the situation is hypothetical, you can add もし to the beginning of the sentence.

もしタイムマシーンがあるとしたら、どの時代に行って、誰に会ってみたいですか？
If you had a time machine, what time period would you go to, and who would you want to meet?

動物になるとしたら、一日中に寝たいから、猫になりたいんだよ。
If I were to become an animal, I'd want to sleep all day, so I'd want to be a cat.

これらの辞書の中で、もしどれか一つを選ぶとしたら、やはり電子辞書にするだろう。
Of these dictionaries, if I were to choose one, I would probably go with the electronic one.

トムの彼女は優しくない人から、別れるとしたら、私はうれしくになるよね。
Tom's girlfriend is not a nice person, so if they were to break up, I would be happy.