Any Viking (BTW--by 1362 the term was something of a misnomer) sent to explore Greenland and points west would have known that his safe trip home had to be by ocean-going boat, and had to be east. If one is to believe the Kensington story, the self-same Vikings abandoned their ocean going boats and hiked/canoed hundreds/thousands of miles inland, west, for no discernable reason, ending up in central MN where they had nothing better to do than chip out a message on a hard granite rock.
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.
Their ocean-going boats could easily have made their way into Hudson's Bay, up the Nelson River to Lake Winnipeg (where several islands have reportedly yielded Viking-style artifacts), then up the Red River of the North and one of its tributaries into Western Minnesota.
The land between the Red River and Alexandria is very flat and poorly drained. It would have been essentially submerged during Spring floods and a boat could have been floated literally to the base of the hill.
The granite in the stone is said to be a match for rock found in the Canadian Shield, around Lake Winnipeg.
Net:net -- any Viking travellers didn't have to travel overland to get to what is now the hill outside Kensington.