Humans began sailing the seas over a hundred thousand years so I believe most native Americans came to the New World by boat. If you have to move yourself, your family, and everything you own then a boat makes a much better option than tracking by foot through frozen, shitty tundra.
I knew a Native American anthropologist in a former life who agreed with you. He pointed out the remnants of civilization in the warmer climes of the Americas and asked why there were none along the popular Bering Land Bridge route.
Boat parts and ancient trinkets throughout coastal north America prove that transoceanic voyages occurred frequently. In the northeast, items from the 3rd century were preserved by nature, and then found by modern contemporary prople.
The boats and ships didn’t always survive the trip here, or the return trip, but left evidence of their existence. A 1715 fleet perished in a hurricane off the coast of Florida carrying Billions in gold coins, gold, jewelry, the dowery of the Queen of spain. Those items get pushed on shore during hurricanes.
Historians tried to tell us that trans oceanic travel couldn’t occur back then, but they were wrong. Very wrong. People like to and often need to move. Nations seek riches and will exploit anyone they can to acquire those riches in whatever form they come in to fulfillthose desires or needs.