Visa1:
Yes, during the POE, the US Immigration officer did ask me to surrender the Canadian PR cards to him. After I insisted that I would be surrendering my Canadian PR cards in June, after moving to the US, he checked with his supervising officer and backed off. He did mention that he had put a note in my file to the effect that I had a Canadian PR and would be required to surrender it within "a reasonable time".
Since my POE I have travelled between USA and Canada several times. Usually while entering the USA through Pearson airport it has been very smooth, as I now have the plastic card (even without the plastic card it was smooth - I showed the I-551 stamp on my passport). Each time I explain to the US officer that I got the Green Card recently, I still live in Toronto, and will be moving permanently to the US in June, and in the meanwhile I am travelling to the US to work. I have never faced any problems during the US entry with these answers, which by the way, are absolutely true.
Except the first time, none of the US officers have asked me to surrender my Canadian PR.
On the Canadian side it has been smooth except for one occassion. Usually I present my Canadian PR card to the Canadian officer, and sometimes the officer will just scan my card and send me on my way. If I am asked about the purpose of my visit to the US, I answer honestly and say that I got a US Green Card recently, and will be moving to the USA in June and giving up my Canadian PR. Usually the Canadian officer is okay with this after checking my details on the computer. On one occassion I was asked to go for secondary questioning in a seperate hall, where another officer asked me the same questions, checked my Canadian PR card as well as US Green Card, entered some notes into the computer, and then sent me on my way.
As I am genuinely planning to surrender my Canadian PR so as not to jeopardize my US green card, I have little to worry about. The trick is to keep the answers honest and consistent, so that they do not find any contradictions. Also, you must keep in mind that they have access to each other's systems, so the answers must be honest and consistent on both sides. In end-June I will stop travelling to Canada, and then this weekly encounter with the immigration will stop.
Prithis