I think from all those only a few are actually canonical in some way
Nanoha x Yuuno, romanticl (A's epilogue hint, Manga hints)
Nanoha X Fate,romantic (S1/S2 hints , sound stage)
Erio X Caro, romantic (Strikers anime hints)
Subaru x Teana, really close friends/romantic (Manga hints, a little in anime)
Hayate x Vita, romantic (A's hint)
Hayate x Acous, romantic ?? (not much really for proof)
Anything else? i dont have all the sound stage so might miss some hints thrown in there.
__________________________________________________ __________________________________________________ _______________
Erio and Caro is the most obvious for romance development so far with Nanoha/Yuuno as second followed by Fate/Nanoha (am being serious based on the manag/anime,not trying for ship war here)
-Erio and Caro pretty easy to see
from all the hints in the anime.Very close to each other with some similarity in their unhappy past.Erio being quick and confident boy compliment Caro slightly timid and clumsy personality.
-On Nanoha and Yuuno, if you look at the manga and animes.It seems to be 1 sided so far on Yuuno.
Everything mentioned the A's epilogue was only confirmed by Yuuno not Nanoha so far.When they are together the only person that blush all the time is Yuuno.
They are nice pairing though,Yuuno knew a lot about Nanoha and he was one of the reason she is able to achieve everything so far.
-Nanoha Fate , now am not a yuri fan so i can describe this well.There is quite a number of hint that Fate might consider Nanoha more than just a friend especially in sound stage (although that SS could be interpreted differently). Very suitable match up both in personality and combat
Both NxF and NxY pairing seems to be 1 sided so far , either Nanoha consider all of em as equal friends,not interested/never thought of romance or she is just plain thick.