Those two will be akin to crossing a cow with a goat. different species, no go by natural means. There are many small C. maximas that you could cross with Atlantic Giant or large C.pepos that you could cross with Triple Treat. Only the offspring show the results of crossing.

Wasn't really thinking of crossing those two...really...poor example ..though the cross I make this year, the small pumpkin under the female flower polinated, it wouldn't show any sign of the cross when it developes and I would have to wait until next year to see any result of the cross from the seeds which are produced, right ?

right, only the children pay the price.

Another way to look at it is the pumpkin was there before you pollinated it,(the little bump behind the female flower) so it is the Maternal tissue, same as the plant. The seeds have DNA from both parents, so they will show that next year when you plant.