At its annual meeting in Cambodia, the committee deferred a decision and asked Canada to refine its submission for the area, called Pimachiowin Aki (pih-MATCH-oh-win ah-KEE').
UNESCO advisory groups have raised questions about whether the area is unique enough to warrant a designation as a world heritage site.
The Manitoba and Ontario governments have poured millions of dollars into the bid, and have said they will continue.
UNESCO already recognizes almost 1,000 places around the globe as world heritage sites.
Another Canadian site won recognition at the UNESCO meeting — the Red Bay Basque Whaling Station in Labrador.