Canada didnt have to worry too much in the past, oceans on each side and most illegals would rather stay in the USA. With Trump if he clamps down Canada could get upto 10 million illegals, recent changes in baby bonus and other policies make Canada more attractive. Wire deposit of welfare also makes it easier to spend winters in their countries and the frequent use of similar names makes it easy to collect welfare in multiple names. 
There will be major problems in health care availability and perhaps even a collapse when the costs become unmanageable with too many users on welfare...