He may not have traveled by canoe, at least that far.
Back then the sea levels were a lot lower, leaving more land. It’s not inconceivable that his trip was no more than a couple hundred kilometres. It’s possible that the more eastern point of Asia was within sight of the most western point of Alaska.
If Sarah Palin lived back then, she really would have seen Russia from her back door. :)
Note, the ocean levels were lower but not that much lower ~ as the last Glacial peak period began ending about 14,000 years ago you had a rather rapid increase in world ocean levels. That slowed during the Younger Dryas, then it took off again reaching roughly the current level about 8500 years ago.
There are variations over time.
A much better bet than kayak for getting from Japan to America is to get a ride on a mass of debris created in a major (once every thousand years) tsunami. Should be able to survive the trip provided there aren't too many folks coming along. Such a tsunami should create plenty of opportunities to hop off along the PAC NW or Central American coastlines.
Ydebris flow from japan tsunami ~ do that look up on Google and you’ll get just all sorts of animations.