I'd say
60% Itsuki
30% Yotsuba
10% miku.
As a Nino shipper I hate to admit it but she wouldn't make that kind of expression in that situation.
Ichika's leg is still injured but, like in Nino's case, it would be out of character for her to make that clumsy pose waiting for the kiss although the expression is a good match.
With what Miku said to Ichika in this chapter I'm more inclined to assume she's going to try taking things slower from now on, also I don't think Miku's eyes have ever been drawn the way the bride's were on page 5 aside from when she's imitating one of her sisters. Other than that, just because Fuutarou recognized her once doesn't mean he can do it every time now so there is a chance I'm misreading things and it's Miku after all.
Yotsuba is the one I can most easily see running up to Fuutarou and waiting for a kiss in such a clumsy way and she's made expressions like the one after they kissed a few times before. Yotsuba hasn't showed any noticeable romantic interest in Fuutarou so far which is exactly why it would be a good twist (and we need more Yotsuba).
The closest thing to romantic intrest in Fuutarou Itsuki 's shown is her comment about hiding things she made this chapter and, just like Yotsuba, that previous lack of interest is why it would make for a good twist.
Now here's the thing nobody else has mentioned yet!
Nino has mentioned before that Itsuki always talks in keigo which is more formal and polite than most people would talk around family and close friends (or when shouting to yourself about how hungry you are a few chapters ago). However, on pages 20 and 21 when the sisters are talking to each other every line said is spoken causally in the raws which means one of three possibilities.
1) Itsuki fixed her habit of always using keigo.
2) Itsuki just happens to have not said anything in those two pages.
Or 3 and most likely, Itsuki is the bride and so of course she isn't in the room.
There's still the mystery of the multiple rings and wedding dresses (harem) and there's always the possibility of asspulls from an author but it's looking pretty damn likely that the bride and the one who just kissed Fuutarou is Itsuki.