Ammo, a word of mouth agency, was acquired by Isobar in 2006. It is headquartered in San Francisco with offices in New York.
Ammo's Toronto outpost will be supervised by Daren Trousdell, COO of Isobar Canada.
Aegis said the agency's vision and global strategy will continue to be directed by Ammo president Julian Aldridge.
Ammo's clients include Beam Global Wine and Spirits, Electronic Arts, Reebok, Philips and TiVo.
Aldridge said: "CMOs are increasingly looking to increase their return on marketing investment so influencer marketing is taking a larger slice of the media spend.
"Word of mouth recommendation is the number one factor influencing purchases in every single consumer category, and since 78% of those recommendations happen face-to-face, marketers have to engage in those conversations offline as well as online."
The launch is the latest in a series of moves which have seen Aegis expands its presence in Canada.
In June 2008, Isobar opened search marketing agency iProspect, and in the previous year acquired digital marketing firm Mindblossom. Both are based in Toronto.