If you're interested in giving some sugar popcorn a try, here is how you can ask for it in French.
Je voudrais du popcorn sucré s'il vous plaît (juh voodray dew popcorn sook ray seal voo play)
Translation: I would like some sweet popcorn please.
This is how you ask for the savory kind with salt.
Je voudrais du popcorn salé s'il vous plaît (juh voodray dew popcorn sal ay seal voo play)
Translation: I would like some popcorn with salt please.