Just returned from my second visit to the US since the NOA1. Both times I said I was visiting my fiance and there wasn't a problem. The first time I was asked when we were getting married and I said when our visa process is complete, hopefully in the fall. I had a copy of the NOA1 and ties to Canada but haven't been asked or questioned about any of that. My advice would be to my honest and look them in the eye. I'm sure it will be fine. Good luck and have a good vacation!