BNO由英國去美國

You should go to the American Ambassador office in U.K. to apply for the U.S. travel visa. I will say likely they do not issue for you, and they will tell you to go back your home country to apply. This is better for you to apply for the U.S. travel visa in Hong Kong. Now, you do not need to make the interview by the U.S. officer, and you just pay the application fee together with your BNO to put it in the box. You can get it back tomorrow. Also, you will submit the employer's letter to prove your employment and annual leave period or days for your application. About 70-80% applications are successful. Good luck.
By the way, if you do not have the U.S. travel visa, you do not try to go there via Canada because you will be rejected to get in. Even you are inside the car, you need to get off, and back to Canada.

ur now residen of uk.you should submit your application in London.
give them a call london.usembassy.gov/

如你不是在英國工作或讀書，美國駐英領事館應不接受申請，因為這與在加拿大旅遊想用 BNO 申請美國簽証一樣，美領事館也要申請人返回原居地再申請，他們會質疑為麼不在出發前辦好簽証。