Boeing (NYSE: BA) boosters might want to get their rotten tomatoes ready. For as long as I've been writing about the competition that foreign plane builders pose to Boeing, I've faced heckling from the company's fans. I don't expect that to change today as I talk about some happenings in Canada.

There are many reasons to doubt Boeing's ability to remain one of just two dominant global airplane builders. SAIC and AVIC are building new jetliners that threaten to steal Chinese demand for Boeing 737s. Japan's in the race, too, and Russia. But the biggest looming threat lies just north of the U.S. border, in Canada, where Bombardier's C-Series airliner is starting to gain traction.

When I wrote about the C-Series last year, Boeing boosters groused that the C-Series had only sold "90 planes" after six years of trying. But that was then. After landing several new buyers at last week's Paris Air Show, Bombardier now sports a customer list stacked with brand names including Lufthansa and Republic Airways (Nasdaq: RJET). Counting orders received through Friday, Bombardier has 123 firm orders for its planes. That's a 36% increase in unit sales, in less than a year. What's more, Bombardier has a "letter of intent" to sell 30 planes to Korean Air, and an additional 109 planes on "option" to firm buyers. In short: Bombardier's got momentum. The risk it poses is real.

"We've analyzed their attack, sir, and there is a danger."
Let me be clear: I do not hate Boeing. In fact, at one point, I predicted it could become the best-performing stock of 2011. I love the way it's selling the 737. Sales to jetBlue (Nasdaq: JBLU) and AIG (NYSE: AIG) notwithstanding, I think Airbus's A320neo is overhyped, and no danger to a company that's got a seven-year backlog of 737s to work through.

That said, earlier this month I argued that after a 20% rise in price, Boeing had peaked. And while I expect the stock will pop briefly when it begins delivering 787s to Japan, reality must eventually set in. And the reality is this: Boeing admits its 787 Dreamliner will be unprofitable "for some time." It confirmed last week that it's actually losing money on the KC-76 refueling tanker. Suppliers like General Electric (NYSE: GE) are moving to diversify with sales to Airbus, and to China, -- hedging their bets on Boeing.

You should, too.

Fool contributor Rich Smith holds no position in any company mentioned. Click here to see his holdings and a short bio. Try any of our Foolish newsletter services free for 30 days.

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