I have had this exact problem on a few fords.
The winder handle can take a lot of force and is VERY strong, but this is what I do.
Turn the handle in the direction of pop up whilst gently thumping the , and pushing from the inside rear centre of the glass panel, do this trying up then down(towards slide back), it will eventually work.
Another thing I have done is to use a plastic ruler to go all the way around the panel from outside, inserting between the roof and panel, to break any mould there that is holding it.
If you can get helper on the outside pushing down on the sunroof when tryig to slide back that will help a lot.
tabetha