According to Michael Grange at Canadian site Sportsnet, Toronto general manager Glen Grunwald had the chance to trade the now-fat-but-then-awesome Vince Carter and big man Antonio Davis for both Nowitzki and Nash back in the days of Y2K.
Today, this sounds egregiously terrible, a missed opportunity up there with drafting Sam Bowie over Michael Jordan. But don't let Carter's current globularity fool you: back then, VC was one of the most athletic, aerodynamic players the NBA had ever seen, and the lesser-known Davis was a nightly double-double threat. Ha, the Raps almost even made the Finals with that core! What a time. And on Dallas' end, the up-and-coming Nash and Nowitzki had yet to make the playoffs together. In '99-'00, presumably the year before the hypothetical trade, Dirk posted 17.5 points and 6.5 rebounds on his way to a solid but unmoving 17.5 PER. Nash only played 56 games and was even less impressive, averaging 8.6 points and 4.9 assists with a below-average 13.5 PER—the third-worst of his career.
This means that the Raptors would've been gambling, buying low, banking on the inevitable evolution of the obviously talented young duo. If the Raptors had managed to lock up Nowitzki and Nash, it would've completely changed the composition of the franchise. They wouldn't have drafted Chris Bosh in 2003, presumably, because their record wouldn't have been bad enough to net them the fourth-overall pick. (Unless N+N took a minute to gel, and their record was that bad, and then N+N plus Bosh—the mind reels.) And even though Carter was a force of nature at the time, Toronto only got a few more seasons out of him anyway: VC forced a lopsided trade to New Jersey by the end of 2004. Meanwhile, Davis got dealt to Chicago in 2003 for Jalen Rose. So, the trade looks like a risk when you inhabit the thinking at the time, but hitting on those risky ones are how GMs make their careers.
Nash and Nowitzki played together in Dalls through 2004, making it as far as the Western Conference Finals in '02, where they lost to the Spurs. Despite never winning the title, they were a threat basically every year they played together following that trade-y 2000 pivot. You have to imagine excitable, borderline adolescent Mavs owner Mark Cuban would've loved having the destructive aggression of Vince Carter around to slick his first years owning the team—Cuban bought in at the beginning of 2000—but he would've been short a point guard without Nash, and Carter hasn't had near the longevity that either Nash or Nowitzki has demonstrated. Notwithstanding a couple volume-shooter years with the Nets at age 31 and 32, his career post-30 has been a pale shade of his 20s, whereas Nash and Nowitzki have actually had better fourth decades than their thirds.
Anyway, no Nowitzki = no championship for Cuban. And Nash and Nowitzki together in the primes of their careers, if Toronto could lock them up long-term after the trade, would've almost certainly led to a title for Canada's only franchise, considering both players made it so close without a second-star so many times last decade.