There's been plenty of talk in recent weeks about how the Calgary Centre by-election might serve as either the time for an inter-party pact to limit voters' options opposing the Harper Cons, or a spur to future movement on the same front. But before we accept either of those arguments, let's point out that the same by-election also offers plenty of reasons to doubt the effectiveness of non-competition agreements.
Most obviously, Calgary Centre serves as an obvious case of doubt as to which opposition party is in fact best positioned to win. Two recent polls have shown a close race, but between three parties - meaning that we have very little way of even knowing who has the inside track to defeat Joan Crockatt based on their current starting point. (Keep in mind that the same problem arose in Ontario in 2011: at least some seats where "strategic voters" were admonished to vote Lib ended up as Con-NDP contests.)
And that uncertainty becomes doubly problematic given that even perfect information about which party is currently in second place may not tell us which has the best chance of winning a plurality of the vote. Is the Libs' brand toxic enough to lose Green voters who might otherwise form part of an opposition coalition? Or do the Libs have more ability to win over Red Tory voters who would see the Greens as too extreme? It's almost certainly too late to find out with any certainty - and absent some evidence that one candidate is substantially better positioned to assemble the needed number of voters to win, it's a fool's errand to try to organize votes based on guesswork.
Equally importantly, there's also the question of what a one-time pact would accomplish. The loss of a single seat won't put an end to Cons' stay in power, and Stephen Harper has never shown any inclination to move an inch off his chosen course of action based on concepts such as as "voters sending a message". Which means that even a successful attempt to translate anybody-but-Conservative votes into a by-election win will have a limited effect in practice.
And of course, the return from an added MP has to be weighed against what each other opposition party stands to lose by shedding by-election support. The NDP, Libs and Greens are all running strong candidates who would have been unlikely to pursue a nomination without some expectation that they'd receive the best support the party had to offer. And all three can justifiably see an opportunity to build off the infrastructure developed in the by-election in elections to come - even if the outcome on the 26th is another cringe-worthy trained seal in Harper's fold.
All of which is to say that I don't see a particularly compelling case to treat Calgary Centre as a scenario where parties or voters should set aside their long-term goals for the sake of a temporary celebration. Instead, far better to focus on building as much momentum as possible within each opposition party - with the goal of building opposition among Calgary's general public, rather than settling for a single MP as the be-all and end-all.