We are told to let our requests be known to God, yet it is always the best choice for us to say, "Not my will but yours Father be done". For the Father knows the future plans that He has for us. I have many testimony's of things that I have prayed about because I thought if was for my downfall, yet! to my suprise was turned around for my GOOD.
Phil 4:6 Be careful for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God.
However this was not the case for Jesus. He understood that He came to die on the cross. He was not looking to get out of it, he just knew that him becoming sin (for us) was shameful and would separate him from the Father for a bit(3 days) and he was not looking forward to it.
Heb 12:2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.
2 Cor 5:21 For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him.