We found a random mortgage specialist (a Chinese lady) at RBC. Without knowing the full picture of my brother's income situation, she immediately suggested that she could get the mortgage approved regardless, just needed to fake some documents.
It was astonishing how she went straight to the point so quickly to someone she met the first time.
She also said a lot of people has non-taxed income and needed a way to get a mortgage before the real estate price becomes out of reach.
So definitely not just HSBC.