Will Haven aren't completly unknown in the US but they are not far off. They got a pretty big CA fanbase but still not even that big (their hometown shows rarely sell out). Whatever fanbase they do have in the US it was definetly from their tours with Deftones, Far, Soulfly, Slipknot, V.O.D, ETC
They are kind of same as like Amen where they are from the US but they only have a small cult following here while they are huge in the rest of the world especially the UK