It already exists. It's called Konqueror. Guess what, Konqueror was the first browser to use Webkit. Ever. Actually, let me rephrase that, Konqueror's rendering engine, KHTML, was picked by Apple as the rendering engine for Safari because of its high performance and clean OO code base. It became Webkit because the version they forked and modified would have made it complicated to merge back the changes into the main KHTML code base. This pissed off a lot of people that put a lot of work in KHTML. Eventually the heat died down and the KDE developers simply dropped KHTML to use Webkit because it had a bigger developer base and corporate backing (paid devs).
So please, stop with the "But you can build Webkit on Linux!", we know, we know better than you what we can and can't do with Webkit. We were there when Webkit was born, we used Webkit before it was called Webkit. We know its history and its origins.
Which brings us to :
Wait, you're saying Webkit is the browser, but then saying Apple put a Safari restriction to make sure it displays properly ? Again useragent spoofing, welcome to 1999 and the Web. We're in 2010, useragent spoofing is retarded.
The fact is, Apple could've made their useragent sniffing for Webkit if they wanted to make sure that people weren't using Gecko or Presto based browsers, which both support the Canvas tag in a standard way. The current shipping versions of Chrome, Konqueror, Epiphany all use versions of Webkit that are NEWER than what Apple ships in Safari (yes, Safari is due for an update).
Apple didn't for 1 simple reason : Advertising. Plugging its own product.
So stop repeating all the nonsense you keep repeating because we'll keep repeating the same thing : There is NO SAFARI ON LINUX. Because there isn't. Never was. Never will be (unless Apple gets a brain fart and starts porting stuff like iTunes and Safari to Linux).
For the rest, if you want to see what HTML5 Canvas can do, there are sites out there, one of them is
http://www.canvasdemos.com/. No need to rely on Apple, they aren't the first on the block to support HTML5, people were already jumping on the HTML5 wagon before Apple started pushing it.