N3
としたら・とすれば・とすると
If it were the case that, Assuming that...
来週出かけるとしたらどこに行きたい？
If we were to go out next week, where would you want to go?
Explanation
「としたら / とすれば / とすると」 all mean 'if it were the case that...'. You set up a premise that differs from reality or is not settled yet, then say what follows. 「としたら」 is the most hypothetical, often for ideas contrary to reality or for imaginary questions: 「もし生まれ変われるとしたら、何になりたい？」 (If you could be reborn, what would you want to be?). 「とすれば」 is more written, for reasoning and analysing conditions. 「とすると」 follows a logical line to a result.
Mixed up with
「たら / なら」 can be used for things that will surely happen: 「春になったら」 (when spring comes). 「としたら」 is always an assumption made in your head ('suppose this were true').
After 「とすると」 you cannot put requests or will such as 「～てください」, 「～たい」, 「～なさい」. Follow it with an objective inference or a fact.