In this corner, a 1,500-pound brute capable of crushing a seal skull with a single bite, a white giant with no predator but climate change.
And in this corner, a 1,200-pound brawler endowed with two-inch-long claws and a fiercely territorial attitude.
The bad blood has outlasted 200,000 years of evolution. Internet discussion boards have buzzed about it for years.
And now, it seems nature may soon solve the pressing question: Grizzly versus polar bear, who wins?
A new report offers the first documented evidence the temperamental grizzlies are migrating into polar bear territory. Researchers found that seven grizzlies have been spotted in Wapusk National Park south of Churchill, Man., between 2003 and 2008.
Since then, sightings have multiplied.
"In 2008, I saw the first one I'd ever seen," said study author Robert Rockwell, an ornithologist with the American Museum of Natural History who has been researching snow goose populations around Churchill for 41 years. "But last year, I saw three different ones. Clearly they are settling in."
Those who live in and around the northern Manitoba town, known as the polar bear capital of the world, have noticed the same. Tour guide Kelsey Eliasson said there were at least four confirmed sightings last summer, including one along the famed Polar Bear Alley - this in a province that has listed grizzlies as officially extirpated for over a century.
The grizzlies appear to be migrating south from Nunavut. Some bear experts suggest that growing populations around towns such as Arviat have been forced to spread over a wider expanse in search of habitat. Others believe that warming northern temperatures may be drawing the grizzlies into areas formerly dominated by polar bears.
"It's possible we have a first warning sign of what happens when our large mammals start shifting habitat due to climate change," said Gaile Whelan Enns, director of Manitoba Wildlands.
But more importantly for some Internet geeks, who wins a battle of the ursine antagonists?
"That's difficult," Ms. Whelan Enns said. "The grizzly is more accustomed to the predator-prey relationship, whereas the polar bears are not quite as aggressive."
They are, however, the world's largest carnivore, often outweighing their grizzly brethren by 500 pounds or more. Despite that, a large body of online authorities sides with Ms. Whelan Enns.
"Polar bears are used to eating seals which are easy prey, while grizzlys [sic]hunt lions," wrote one dubiously informed member of a Yahoo message board.
At boxingforum.com, members have devoted 19 pages worth of comments to the prospective fight.
"I just can't see a Polar Bear winning," wrote one poster. "If a Grizzly uses his claws to swipe blow after blow on the Polar bear, he'll win it. If it becomes a wrestling match with the bears biting each other's necks, the Polar bear would have a chance."
Dr. Rockwell, dedicated academic that he is, has pondered such a tilt at length. He believes the two bears would most likely come into contact around the peat banks that make the only decent denning ground within Wapusk National Park. Because polar bears only den when they're giving birth, the most possible scenario would see a weakened female take on a grizzly of either sex.
"If it's a fight between a 1,200-pound male polar bear and a 600-pound grizzly, I think we know who would win," Dr. Rockwell said. "But in this likeliest of cases, it's debatable. There are actually reports in the literature where grizzlies have killed denning polar bear females."
There are also reports of the distantly related bears making love rather than war, points out Canadian Wildlife Service polar bear expert Nick Lunn. In 2006, a white bear with brown patches shot on Banks Island was confirmed to be a grizzly-polar hybrid. "I preferred the name pizzly bear," Dr. Lunn said.
But perhaps all the fight talk misses the purpose of the research. "I don't want the message from the paper to be, 'Oh wow, the grizzly bears are going to start eating all the polar bears,'" Dr. Rockwell said. "That's not the point. The point is we've got an expansion of a second bear into that range and there are going to be increased encounters."