Yeah, I was thinking BB would closest fit the "requirements" for Bowser Jr.Walmart -- Mario variations...it might get both Dr. Mario and the other missing 8-bit Mario.
Target is "female oriented", TRU is Pokemon, BB is the "rival", Amazon had the "Amazonian" one (tall, strong woman), GS has had the niche characters.
Out of all of those...I would bet Best Buy would get Bowser Jr. rather than TRU. He's the closest you'll get to another character in the "rival" category.
I so hope Walmart doesn't get any more exclusives. They almost never have any amiibo, or it's all such old stuff.