Do you consider this sermon an "attack on Whitfield?" If not, if it is a general evaluation of the tulip doctrine, then what were his specific attacks on Whitfield?
"I hear, honoured sir, you are about to print a sermon on predestination. It shocks me to think of it; what will be the consequences but controversy? If people ask me my opinion, what shall I do? I have a critical part to act, God enable me to behave aright! Silence on both sides will be best. It is noised abroad already, that there is a division between you and me. Oh, my heart within me is grieved..."
Note that Wesley published this sermon even though Whitfield had pleaded with him not to do so in order to preserve unity. Wesley cared nothing for unity, and showed himself to be a schismatic.
Whitfield certainly felt that this sermon was a personal attack against him, he stated "I have been supplanted, despised, censured, maligned, judged by and separated from my nearest, dearest friends." as a result. Take the time to read Whitfield's letter to Wesley (found here). You will notice, I hope, just how gracious and accomodating Whitfield was in this controversy. If you were to take the time to research all of the correspondence between these two men during this period, you would see that Wesley really was a bit hypocritical to heap such praise on Whitfield at his funeral, especially when he took as many pot-shots at him as he did during his life.