BRUSSELS — European Union leaders will look to boost aid to Greece as the Balkan migrant route is effectively sealed, using Monday’s summit as an attempt to restore unity among the 28 member nations after months of increasing bickering and go-it-alone policies, according to a draft statement Sunday. The leaders will also try to persuade Turkey’s prime minister to slow the flow of migrants traveling to Europe and take back thousands who don’t qualify for asylum. In a draft summit statement produced Sunday, the EU leaders will conclude that “irregular flows of migrants along the Western Balkans route are coming to an end; this route is now closed.” Because of this, the statement added that “the EU will stand by Greece in this difficult moment and will do its utmost to help manage the situation.” “This is a collective EU responsibility requiring fast and efficient mobilization,” it said in a clear commitment to end the bickering.