What I red on this forum yesterday, this "flag poling" doesn't work any more (at least at Niagara Falls bridges). You have to get entirely to the US side (you need US visa).
Sorry I don't remember in which thread it was written.
The U-turn thing is not available any more. Even administrative refusal is not working now. What I heard you need the US visa and get entirely to the US side. After that you can get back and complete your landing.
There were guys on this forum who stopped at service Canada on their way back from landing and got their new SIN. Maybe it depends on the person you are dealing with.
What you did was correct.There were some applicants in this forum before, who even enclosed similar letter you received from HRSDC (to support their NOC number selection) and were refused because a VO was not satisfied with their number. So be cool.