"The dollar stores are nipping away at the drug stores, grocery stores, Walmart," said David Ian Gray.
Dollarama has 900 stores across Canada and is opening 70 to 80 more per year. The Montreal-based company saw profits increase last fall.
A competitor, Dollar Tree, is also growing. It now has 200 stores in Canada, up from 86 in 2010.
"You know that when you come to our store, you're gonna get great value whereas in the past I think people figured if I don't go to Walmart or a big box store, I'm gonna be paying too much," said Joe Calvano, president of Dollar Tree Canada.
Calvano founded B.C.-based Dollar Giant in 2001 in Burnaby before selling the company in 2010 to Dollar Tree, a much larger American company.
Gray said dollar stores are offering more selection now, including canned food and snacks.
"Walmart is concerned because there's still dollars that could be spent at a Walmart that are now sliding to other formats," he said.