That is not totally correct. You will have to declare this everytime you want to enter the US and it will be on your record with the US immigration.No. I have read many forums.. It does not impact your future travels..
It will not show in your passport
It doesn't mean that future travels will be impossible but saying that there is no impact is a bit far fetched. You will have to explain this administrative refusal to the USCBP every time you go to the US for the rest of your life.
If you can, it is recommended to enter the US (especially if you are from a visa exempt country) and go for, let's say, shopping before getting back into Canada.