Since there was talk about it on the last few pages, I'd like an Avatar crossover, because it's always fun to try and guess who would get what type of bending. So, my suggestions:
Lalli: the Avatar, since the comment section already concluded that he entered the Avatar state when he was dragged under water, what with the glowing eyes and all. Plus, he's also a kind of bridge between mortals and spirits. (I'm guessing his starting bending could be Waterbending, but this is mostly because of his color scheme)
Braidy: Airbender. His personality (as it seems for now) fits, he has a connection with the "spirit world", and just look at him jumping across that lake light as a feather.
Tuuri: Metalbending! What better ability for an engineer to have? A practical and grounded form of bending would suit her nicely, and I guess it would help with her repairs and driving.
Emil: Need I say more? Firebender. It would probably be a dream come true if he had the ability to shoot flame bolts out of the palm of his hands. Just imagine all the things he could destroy! Also, he's in the military and values his status and self-image over all else *khm*HONOR*khm*
Mikkel: I couldn't make up my mind. My first guess would be Earthbender, but his role as the group healer and his versatility make him a viable Waterbender, too. Changing his jobs and roles would fit the whole "water is the element of change" deal.
Sigrun: A badass normal non-bender that makes up for her lack of bending with her pure awesomeness, combat prowess and foolish heroics.