Canada apparently wants a 5th Generation fighter, which severely limits the existing pool of candidates to pretty much the F35. The Rafale, Typhoon, and other theoretical options fall into the 4.5 to 5 gen categories, but are not quite at the technological level of the Lightning II.
The iPhone 4 is superficially the most advanced smartphone available today. It's without doubt a capable technological marvel and has a number of features that it's ancestor and competition don't. And like most Apple products, attracts its share of giddy fans (caveat: I like my mac) willing to line up for hours or pre-order in thousands. But lo and behold, this awesome device suffered a basic flaw in with design and location of its combined antenna which has meant signal loss and pissed of users. So much so that Consumer Reports is recommending the older model 3GS over the 4. The flaw did not emerge until after the phone hit the market and users discovered. Apple's initial response was a flippant "you're holding the phone wrong." Sorry, but we've been using phones for about a century now, and their ergonomics are well known. It doesn't matter what sort of contract subsidy gimick Lockheed Mar - sorry Telus or Bell, offers on F3 - I mean iPhones if the thing suffers a basic functionality issue that remains unknown until it's put into service.
While the F35 is arguably the only 5th generation fighter aircraft on the export market today, this doesn't necessarily make it the best option. Nor does it mean it will remain that way forever. Sure it's got a whole suite of features that competitors may not, but this does not necessarily translate into operational viability when the full spectrum of aircraft systems and performance are matched with user's specific operational requirements. And certainly doesn't factor underplayed or unknown design flaws that may yet emerge in production aircraft. Being the sole available 5th generation fighter on the market, the F35 is the guinea pig. From this point on, anything following it will improve upon the problems emerging in operational F35s.
Even if the Air Force thinks the F35 is the best and most cost effective for its needs and it really could be...again, we can't be sure without a rigorous trial comparing it to other aircraft. I seem to recall a recent submarine purchase that looked so good on paper but killed a sailor on the voyage home and have required a considerable bit of work since.
There's a much larger point in here about the nature of technology. We tend to culturally labour under the impression that higher tech and more advanced equates to better. In areas like computers and military capabilities tech innovation drives tech innovation in a race. As a counterpoint however, the most technologically advanced array of military forces in history are unable to cope with a persistant and low tech insurgency in about the poorest region of the planet.
Tech isn't linear. Relying on it too much is dangerous. It'd be interesting to be a fly on the wall after an exercise (and I would hope this would happen only at the exercise level) where 4th generation a/c 'enemy' force pilots get clever and figure out how to knock down their 5th generation counterparts.