This is a fluid situation and we don't have all the relevant details, including what the immediate future holds for incumbent quarterback Kevin Kolb. Stanton played under Cardinals coach Bruce Arians, so he'll come to Arizona knowing the offense.
I've put together a chart showing how Stanton has fared in limited chances since making his NFL debut in 2008. The chart shows stats over the same time period for Kolb and recent Arizona quarterbacks Brian Hoyer, John Skelton and Ryan Lindley. None has a Total QBR score in the 50-point range representing average play.