Comment by proberts
There's no question that it's tougher now to get into the U.S., whether from Canada or another country via pre-clearance or via a land crossing, and there can be significant differences among airports and land crossings. Canadians are unique because they are visa exempt and CBP feels particularly emboldened to reassess their admissibility every time they enter. The keys are to avoid bad pre-clearance offices and land crossings and even more importantly to carry the right paperwork, which varies depending on the specific status being sought. There is also a huge difference between seeking entry as a visitor versus seeking entry as a worker with a visa, with the former much more challenging now.
Could you give some examples of "bad" pre-clearance offices?