Meanwhile, today, Frontier applied for government authority to fly to Canada starting around May 24. The carrier now flies only domestically and to Mexico. It may fly to Canada with its own aircraft or under its code-share agreement with Horizon Air.
Further, Frontier plans to expand to at least three new cities this year and will add more than 20 flights on existing routes.
http://www.denverpost.com/business/ci_3375029
Since Southwest Airlines doesn't fly internationally, further international flights from Denver is a logical way for Frontier Airlines to help deal to the appearence of Southwest Airlines into the Denver market. Along with business travelers, and Denver leisure travelers to Canada, I would expect another major segment of the market for Frontier will be connecting Canadians to to Frontier's various resort destinations in Mexico through their Denver hub.