One advantage both Montreal and Vancouver have, are existing teams with rich histories:
The Whitecaps have been around for roughly 35 years, and are the oldest professional club in North America. They have a billionaire owner and now Steve Nash NBA MVP, (who has been a Whitecaps fan since he was 6 yrs old) is on board.
MLS have already approved their plans to move into a renovated BC Place. Back in the day of Empire Stadium, the Whitecaps used to draw crowds of over 20,000. They are former champions in the NASL, CSL and now USL First Division. They also beat TFC at BMO Field, and tied them in Vancouver, in Voyageurs Cup action. Not to mention beating the LA Galaxy in Edmonton in front of over 30,000.
The Montreal Impact just opened their new soccer specific stadium, Stade Saputo. It's a beautiful 13,000 seat stadium, and the pitch is said to rival anything in the world (unlike TFC's BMO Field, which has FieldTurf). Plans are already in place to expand to 20,000 seats. Montreal are former USL First Division champions, and seven time Voyageurs Cup winners, beating TFC at BMO Field this year to claim the Canadian championship. Montreal in USL regularly out draws MLS clubs. They are also owned by the Saputo family, which are worth billions and are the fifth richest Canadians.
Any new club (including Ottawa) starting from scratch can't touch any of this.