Director of soccer operations Soehn took over when Teitur Thordarson was sacked in May but will step aside for Rennie who has signed a three-year deal from NASL club Carolina RailHawks.
The incoming of Rennie means that Thordarson's assistants, Colin Miller and Dennis Hamlett, have lost their jobs with the new boss set to bring in his own coaching staff.
Scottish-born former Canada international Miller admits he is disappointed but understands that it is purely a decision based on the good of the club.
"I've been in professional football for 30 years and I know it's not a personal thing," Miller said.
"It's a professional thing that Martin wants to bring his own people in ... I knew as soon as they appointed Martin that the writing was on the wall for me.
"It's just part of professional sports. I'm obviously gutted about how things have developed but I'm certainly not bitter."