Canada promised Trump a border crackdown. Easier said than done.

* Canada promised Trump a border crackdown. Advocates warn restrictions could put migrants at greater risk * Canada faces 'credibility challenge' on migration, Immigration Minister says By Anna Mehler Paperny SAINT-GEORGES-DE-CLARENCEVILLE, - Six Lego-like concrete blocks mark the end of a rural road at the U.S.-Canada border. "We have a very important activity to undertake to make sure that we give confidence to the U.S. that we have an immigration system that they can manage for," Canada's Immigration Minister Marc Miller told a private meeting last month with the Canadian Council for Refugees advocacy group, according to a recording obtained by Reuters. PATROLLING THE WORLD'S LONGEST LAND BORDER Reuters spent four hours with RCMP officers patrolling part of a 105-mile stretch of the border known for frequent migrant crossings, watching out for tips from the public; calls from U.S. authorities; suspicious movement captured by surveillance cameras and erratic drivers suspected of carrying potential crossers. Canadian law enforcement is bracing for a potential influx of migrants fleeing Trump's threat to carry out mass deportations once he is in the White House, Poirier said.