There was a study published in Nature last year [1] that concluded that it took hundreds of years after the ice sheets receded and the route become passable before plants became established, and then later animals, to make it possible to survive off the land during such a trip.
We know that the Clovis culture was established before then, so if they or earlier people came by the land route then they must have brought their supplies with them.
That was before the invention of the wheel, so if they brought all their supplies with them for the journey it wasn't on wagons or carts. They only animals they might have had to help carry things were dogs, because no other animals were domesticated at that point.
So we're looking at carrying everything they need for the trip on their own backs or on crude sleds, possibly with the aid of dogs (and if they are bringing dogs, they have to bring all the food for the dogs, too).
This just seems to me to be too farfetched.
Now compare to coming by boats. With boats it is easy to bring plenty of cargo. Whatever food they bring with them can be supplemented with fish and other seafood they can catch on the way. Maybe they can even live entirely off seafood.
[1] I haven't seen the study itself freely online, but here's an article that goes into detail about it: http://www.history.com/news/new-study-refutes-theory-of-how-...