The natives traditionally called the beast saytoechin, which literally translates to "beaver eater." When shown pictures of similar-sized potential relatives to the beaver eater, eyewitnesses have uniformly identified the creature immediately: the megatherium, or giant ground-sloth.
This ugly sonofabitch right here.
The size and appearance of the ground sloth matches the saytoechin perfectly. There's just one problem: the giant ground sloth has been extinct for over 10,000 years. The beaver eater has been sighted as recently as 1989. There's a slight discrepancy in the dates there.
Could the saytoechin be a surviving megatherium? It's not like theories that the Loch Ness Monster is a surviving aquatic dinosaur from 100 million years ago. Ten thousand years is not that long. Is it long enough for the herbivore giant sloth to develop a taste for beaver? Possible, but it's a long shot.
About as long of a shot as me getting through this post without making a crass joke.
Other, slightly more plausible if less fun theories about the saytoechin is that it could be just an unusually large grizzly bear, or a short-faced bear (Arctodus Simus), which although also extinct is at least a carnivore.
A super-weird theory is that the Yukon Beaver Eater is actually a giant beaver itself (a castoroides), which is probably the most terrifying idea of all. We're talking about a 2-metre plus (7-foot) long beaver, weighing hundreds of kilograms, that is also a cannibal? I'm glad Canada doesn't have things like poisonous snakes and giant spiders, but I think a giant cannibal beaver might be just as bad.
Yeah, no thank you.