It works sporadically where I live in Canada. Sometimes people get it, other times they think you’re trying to cut traffic. A few locations even have signs “recommending” it on some of the more congested merges in our city.

Also, laws vary by state/province, my province says merging must be facilitated by both vehicles (so cars can’t be dicks intentionally) so neither vehicle has the “right of way” automatically, but other places don’t. So you could speed up to cut someone off who’s trying to merge and wouldn’t technically be breaking the law, just an asshat.