"either will do" is both correct and usable in written English.
It is often used to express that two options are equally acceptable or suitable. Example: "Would you like tea or coffee? Either will do."
"Either will do," said Mr Bean.
Scarlett Johansson has a striking face and a resonant voice, though it seems that either will do.
Wood will eventually be eaten, and plastic cracks easily, but either will do in a pinch.
Either will do if he wants to block a trade.
Either will do, but I'm sticking with lemon; it just works better with these classic flavours.
"Either one will do fine".
One thing I can say, though, is that Democrats and like-minded independents are optimistic that either Democrat will do well against the likely Republican nominee, Senator John McCain of Arizona.
"Editors and authors can be confident that either group will do an adequate job at reviewing the manuscript," says Schroter.
Of course, the defenses on either sideline will do everything they can to keep both those offensive playmakers from being the heroes in this one.
