Unfortunately, there just isn't any game that's like COH. I suppose the closest thing I can think of that's good is the Wargame series, which is excellent. It isn't like COH, though, but I highly recommend it.
As someone already suggested, the Modern Combat mod for CoH.
However, right now there is another similar game but it's not RTS, it just uses CoH's top down perspective and is similarly looking and playing, sort of but set in the same sort of era as well, it's called Foxhole.
Another game that's due to come out is Iron Harvest: 1920+ heavily inspired by CoH, the devs even said it themselves.
Another alternative would be Hell Let Loose, due to release next year, which again mentioned by it's devs is heavily inspired by CoH for it's commander/RTS part and by Red Orchestra 2 for it's gun play and First Person part.