The club will enter the competition in 2011 and Garber expects the Impact to be a success, following on from fellow Canadian club Toronto FC.
"Montreal is one of those, we're pretty focused on that 19th team, we've been in discussions with Montreal," Garber said.
"We've got a great success in Canada. Toronto FC plays in a new stadium in downtown Toronto. Every game is sold out. 15,000 people on the waiting list for season tickets.
"Montreal will probably be a market that looks like that. And joining Vancouver which comes in '11 we'll have three teams in Canada. That's a market that's been in deep discussions with us. Not there yet on the 20th team."