Will Godzilla Battle Biollante in Gareth Edwards' American Version?

I don't think so, but the author of this article does.

Really it's more conjecture, as the author is basing this off of the fact that the artist who sculpted the rumored Godzilla-design statue (Hecter Arce) also showcases a redesigned Biollante
sculpture on his website.

But if one were to inspect the rest of Hecter's website, one would also see sculptures of Venom, Spider-Man, some werewolves, and so on.

Does this mean that all of those heroes/villains will be in the Godzilla film too?

Of course not, but one can see where this conjecture comes from.

Personally I strongly feel that Legendary Pictures will not use a Toho villain within the movie.

While it's inspirational to consider Biollante (it'd be interesting to see how an environmental message would be linked) Toho licenses each monster for the same price as Godzilla.

In other words it would be very expensive to get MechaGodzilla, Rodan, Mothra, etc., in these movies.

This is one of the main reasons why the 1998 Godzilla did not feature any other kaiju.

Rather I fully believe that they will create an all new monster in order to a) not pay further fees, and b) have the monster vs monster fight we've all been clamoring for.

In any case here's the original article for further reference:

movies.yahoo.com: Will Godzilla Battle Biollante in Gareth Edwards' American Version?