These are not lawyers if they advised that.
As an LPR, legally you have to be admitted. https://www.aila.org/File/Related/18110604b.pdf
Happens all the time in Pakistan now, and rumors day sometimes in India.
Have never heard of it happening from
the UK
Advice: try a different airline, or get an eTA to fly to Canada, and enter by land or fly from Toronto Island airport to Newark.
Yes.