I would suggest the concentration of power within the PMO is effectively creating a separation between the "Executive" & "Legislative". So while Harper is the Majority leader & PM he has also taken upon himself inconjuction with the PMO to be "pseudoPresident". While it can be argued all PM's have had that type of power none have used it to the level Harper had and does. Most PM"s used the Privy Council the Harper uses the PMO.Since when is Harper and the Conservatives leading Canada to a US style of Government? There is no evidence of that statement and it is just another scare tactic those who don't like the Conservatives would use. Try to stick to truths, you might have more success. It is true that the Conservatives would like to see an elected Senate, but that is a little more democratic having the Canadian people elect our Senators and say how long they can serve.
The conservatives are probably more supportive our our constitutional monarch and I haven't seen anything that suggests that that the Conservatives want to go away from a representative democracy.
To me the pecking order looks something like this
1) Harper
2) PMO
3) Privy Council
4) Cabinet