Canadian Prime Minister Justin Trudeau, who was verbally attacked by Mr Trump over trade, also said the current USA policy of separating child migrants from their parents and detaining them is "unacceptable".
More than 2,000 immigrant children have been separated from their families since early May under the Trump Administration's new "zero tolerance" policy, under which adults have been prosecuted for a federal misdemeanor while children were placed in juvenile facilities.
Calling the measure "somewhat preemptive", he also called on Congress to work toward a more permanent fix.More news: NBA Mock Draft 9.0
He added that: "We want to solve this immigration problem". We can enforce our immigration laws without breaking families apart.
In a televised roundtable with members of Congress, Senators and members of his adminstration, Trump announced: "we're going to be signing an executive order. we're going to keep families together, but we still have to maintain toughness or our country is going to be overrun". This "zero-tolerance policy" applies to all adults, regardless of whether they cross alone or with their children.
One of the US Border Patrolfacilities was opened to US media on Monday (local time) and reporters described how hundreds of children were held in a series of cages created by metal fencing.
Trump was headed later Tuesday to Congress to huddle with Republican lawmakers, many of whom are deeply uncomfortable with the separation policy. The administration wants to keep children in custody with their parents indefinitely. The Republicans want security and insist on security for our country and we will have that.
The Trump administration has been charging people with crimes even if they cross the border and claim asylum.
Since Attorney General Jeff Sessions's announcement that all illegal border crossings would be criminally prosecuted, thousands of children have been taken from their parents at the border, sparking an outcry over human rights abuses. One official said it was the Justice Department that generated the legal strategy that is codified in the executive order, and disputed the notion that Homeland Security was involved in drawing up the document.