There is some debated hard evidence, and more circumstantial evidence, about Austronesian, specifically Polynesian, Pre-Columbian contact with the Americas.
The range of this evidence is quite large, but mostly problematic. As far as I know, the chicken bones found in Chile that were originally thought to be of Polynesian origin are now supposed to be European. Also, the closest bit of land were the Polynesians surely is Easter Island - and from there, Chile is arguably near the extreme range of viable reachability with Polynesian tech.
Yeah, I know of Thor Heyerdhal's trip from Peru to Tahiti - but even if similar trips happened ITL, we can assume they were marginal events, i.e. they were about some explorers or very small groups rather than actual colonising expeditions.
OTOH, we know that th Polynesians got the sweet potato from America at some point and somehow - while they didn't apparently leave any of their own crops in the New World; there's evidence of Polynesian coconuts in Tropical America (namely, in Panama and Colombia IIRC) that is likely to be pre-Columbian, but I don't know whether it was a domesticate for Native Americans there (and of course, coconuts can float in the ocean and spread without direct human contact).
Other hints of Austronesian presence in the Americas have been suggested in southern California.
However, from what I found in the Web and in my readings, places and times of contact, if contact occurred at all, are sorely il-defined.
So, what are the areas of the American Pacific coast where the Polynesians are more likely to have arrived, when, and to what impact?
What consequences are likely to be if earlier or more sustained contact happens, and what circumstances can be conducive of such?
The sounder proposal, intuitively, seems to be some low level exchange between Easter Island and South-Central coast of Chile, in almost immediately Pre-Columbian times.
Easter Island, however, was pretty damn isolated and marginal to the rest of Polynesia. Was it a viable route for the spread of sweet potato, for instance?