We need a relatively porous border, because both trade and migration require it.
We need a border where goods can be processed not where millions of people can wander around the country; like they are in NYC.
While Mexicans can walk across the border the reverse is not true . From Loit & Murguia Mexican immigration attorneys
illegal immigration is a felony under Mexican law. In fact, Article 123 of the General Law of Population mandates that “a penalty of up to two years in prison and a fine of three hundred to five hundred thousand pesos will be imposed on the foreigner who enters the country illegally.”
Turning it into the Cold War East/West Germany border would cost far more than the costs of illegal drug importation and illegal migration.
The cost of illegals in NYC alone is $4b per year. Over 100,000 people per year die of drug overdoses. The cost of the lost lives is hundreds of billions of year.
https://www.foxnews.com/us/crisis-kensington-drug-users-flood-streets-lawless-philadelphia-neighborhood
https://www.foxnews.com/politics/illegal-immigrant-charged-murder-released-new-york-police-paperwork-delay
We could seize and interrogate every Canadian trying to enter the country, and doubtless intercept that many more criminals, terrorists, and associated nogoodniks
We already check everyone coming in from Canada & send back those without proper documentation.