No. You don't need US visa for landing. Just tell at US side of bridge that you are here for Flag poling. They understand that quite well and they will give you direction to go back to Canadian side with a paper in your hand.
No. I can see from your signature that you are CEC, so for CEC, they don't ask for POF. The only documents they asked me was my passport and COPR. I still carried my bank docs + pays tubs etc for be on safer side.