Both. That is, all three have the same meaning. There is no significant difference between the participial phrase and when and if in the limited context given.
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AnonymousA: When you turn the left, you will see the department store.Hmmm... I would omit the.
B: If you turn the left, you will see the department store.
Cool BreezeAnonymousA: When you turn to the left, you will see the department store.Hmmm... I would omit the.
B: If you turn to the left, you will see the department store.
CB