One thing breeders should not do, and if they are, run and run fast! advertise specifically for dry mouthed newfs, or, that they have bred generation to generation and can "gaurantee a dry mouthed newf"
GAG
that is the true sign of someone trying to find a selling point that will catch the eye of an unknowing newbie.
First and foremost, there is no way to actually say how much your newf pup may or may not drool
it may only be when having a drink, or during hot weather.
it might only be when food is present, it might only be when excitement presents itself in any form. It also could be becouse conformation breeders have manipulated the heads like there is no tomorrow, shortening the muzzle and making them look like st bernards or mastiff. if you have this "newer type" you also may be in for a drooler.
some newfs slime like there is no tomorrow, mine have been minimal, only during a drink, or excitement or food.
not a constant thing.
you might want to see what lines they are from and find out how the parents, grandparents and so forth were, you might be able to get some kind of idea.