US/Canada land border - Question about regulation/law

[canvis2006]

Hi,

I received my PR visa living in Toronto, and I went to Niagara Falls to "land" and become a PR.

However, CBSA required me to leave the country (by going to US side) and obtain a letter of "refusal of admission to US" from American CBP...to show that I left Canada....I got that and came back to Canadian side and landed.....CBSA kept that letter.....
This procedure does not effect my American visa/future visits in any way.....just a formality....

Does anyone know what is this law/regulation number between CBSA and CBP?
I just want to know perhaps the agreement number, etc of this regulation since it does not effect future travel to US but is sometimes necessary in order to be able to re-enter Canada by showing exit from Canada at the land border.....

If any experts can perhaps point out the specific law/regulation link where I can find details on this, it will be appreciated.

[dodan]

i must learn it. never heard of it.

so did u have a us visa? then why cbp would deny ur entry? why does ca officer need this letter?

can others please clarify when respnding to OP