Via Political Theory Daily, here is a paper by Eric Kaufmann on the "decline" of WASP ascendancy in the US and Canada.
I think Kaufmann gives to little attention to the view that the dominant ethnicity in both countries just extended its self-definition over time (continuously with earlier processes by which Huegenots became English or Dutch became "old Americans").
Also, I'd like more on the actual current "vertical mosaic". The US is far less WASPy than English Canada, but Kennedy remains the only non-WASP in the oval office. The names of 2008, with the exception of Giuliani, could come from the Continental Congress -- Rodham Clinton, Clark, Gore, McCain, Romney, Allen, Bush. Pretty good representation from an eighth of the population. Some decline.