[endorphone]

At legal crossings, no different than flying into the US. Which, for that matter, is how the vast majority of known terrorists have gotten into the United States -- 100% of the 9/11 terrorists flew into the US.

When there is some sort of equivalency drawn between the Southern and Northern border it is usually founded on absolute nonsense. The Northern border likely sees more smuggling of both people and contraband (e.g. guns) North than the reverse.