The journey would have been through Hudson Bay, so the ocean going boats would not have been parked on the east coast. The journey up (South) the Red River from Lake Manitoba would not have as tough as you think either.
In Spring, the Chinook winds dominate. They come from the NW. Thus a boat travelling generally South would have been on a broad or beam reach, a favorable point of sail for such a trip.
A place has been found to the North that resembles the two skerries (islands) described in the text. Norse anchor holes were also found there, which would not have been done by an Indian. Other artifacts have also been found.
The boats they had were somewhat like the boats Lewis and Clark used. They would likely have been lighter and drawn less. There would have been a mast, a square sail and oars. Where Lewis and Clark would have traveled upstream and generally against the wind, the Norsemen would have had a quartering wind, like the Dhows on the Nile.
I urge you to read a bit more and think about it. The facts seem plausible to me. They suggest to me that you may be pooh-poohing the efforts of brave men.
BTW, I have inherited a trove of Civil War books from a Brother in Law. I'd be happy to talk more about that subject. Also, thank you for disagreeing with me in a civil manner. No civil war here.
You correctly point out that it was not impossible for Vikings to have made it to MN. My point was rather that they had no motivation to do so, and every motivation to go in the opposite direction. Being unlikely, the burden of proof is on those trying to prove they WERE there, rather than on those trying to prove they WEREN'T. I don't think one stone, of "challenged" (to say the least) origin and authenticity, is enough proof.