Suspend the safe first country agreement then and they will line up at legal crossings in greater numbers. In practice, this cannot be stopped entirely until the pressure in the US for them to leave eases. In the meantime, most of them will eventually be deported. Bear in mind that Canada's illegal entry problem is miniscule to that in the US. If the US stopped using illegals as a handy source of cheap labour, particularly in the South West and actually kept rack of people on visas, etc. this problem at our borders would fade to insignificance.