Have the Conservatives ever made a similar deal as the one made to Mike Duffy

The answer is yes..............

At the beginning of the campaign for the 2006 election, an Ottawa lawyer named Alan Riddell stepped aside as the Conservatives’ nominated candidate in the Ottawa South riding. The party wanted to run Alan Cutler, a public servant who had blown the whistle on the Liberal sponsorship scandal, in the riding. Besides, as a candidate Riddell was, to some extent, less than ideal. He had run for the Conservatives in 2004 and lost after the Ottawa Sun ran an embarrassing story about a prank Riddell had played in his student days. (He’d dressed up as a character from Hogan’s Heroes, and I don’t mean Corporal LeBeau. A bit of a no-no, in retrospect.) After he lost the Sun retracted much of its story, but the damage was done. So, under some pressure from the party in 2006, Riddell dropped out, the party thanked him for his efforts, and Cutler became the candidate.

http://www2.macleans.ca/2013/07/05/the-conservatives-make-a-problem-go-away-fund-mike-duffys-not-the-first-case/

So my fellow Canadians it appears that the Harper government makes a habit of underhanded deals.