Natasha,
I don't doubt that North American (note the adjective) supermarkets would mislabel yucca as manioc or cassava, since I've seen some bewildering labels put on herbs, greens, vegetables, fruits and even beans sourced from abroad (just try finding the spices listed in many Dominican recipes, and you'll see what I mean! They're often there, but with different names).
Cassava = manioc = tapioca root. They are not the same as yucca.
Yucca is usually labeled as yucca; it's just hard to find in many groceries. We're lucky here in the Washington area because the larger supermarkets carry it and other things from the Caribbean, albeit not always under the name we know it as in the RD. We also have numerous Latin markets, and thankfully they usually have ALL these things.
Me, I'm partial to yuca frita (see my post under "Dominican Republic"). Better than French fries if done properly! Yum!
Regards,
Keith