Proof of Work is a terrible solution
Hard disagree, because:
it assumes computational costs are significant expense for scrapers compared to proxy costs
The assumption is correct. PoW has been proven to significantly reduce bot traffic... meanwhile the mere existence of residential proxies has exploded the availability of easy bot campaigns.
Canvas fingerprinting would work.
Demonstrably false... people already do this with abysmal results. Need to visit a clownflare site? Endless captcha loops. No thanks
Most bots and scrapers from what I've seen already are using (headless) full browsers, and hence are executing javascript, so I think anything that slows them down or increases their cost can reduce the traffic they bring.
Source? I strongly disagree, and it's not hard to change your browser characteristics to get a new canvas fingerprint every time, some browsers like firefox even have built-in options for it.