I disagree. I think the left does indeed have to merge before we can defeat the right wing Conservative party. The right has merged. The left vote is not perpetually split. Each poll says that Canada is more liberal and left-wing, yet Harper could very well get a strong majority with just 39/40% of the vote. Now if the NDP and Liberals join, their vote would be 56%, a true majority and if they merged we would reduce the Tories down to opposition status.
I think Harper winning a majority this time around will force the Liberals to re-think and do some hard-thinking about how to bring forth a new Liberal vision for the country. Merging with the NDP would be their best best for success in the future.
Sorry in advance for the long-winded response, but here goes:
Uniting the Right was a Herculean task that took years and years to happen, and even though it seems to have gone off generally successfully today, it was still marred by huge infighting (especially on the PC side) and many high profile defections (Scott Brison, David Orchard, etc.). There are still Senators who refuse to join the Conservative caucus in that house, remaining Progressive Conservatives. Early on in the life of the new Conservative Party, it was tanking in the polls and probably would never have formed government if the Liberals weren’t tainted by the Sponsorship scandal and plagued with their own decades-long infighting.
Even then, the two right-leaning parties in Ottawa had much more common ground to work upon than the Liberals and the NDP. The Reform Party/Canadian Alliance was still the new kid on the block. Many of its members and supporters were disaffected former Progressive Conservatives who became disenchanted with the party as Mulroney’s grand coalition of right-leaning interests began falling apart in the late 80s. The divided right through the 90s was a historical anomaly, not a long standing tradition in Canadian federal politics (the federal Socreds having become mostly irrelevant in English Canada decades before the rise of Mulroney). The right also had the benefit of being undivided on the provincial level in most parts of Canada and members of the Reform Party/Alliance were used to working with members of the federal PCs. Remember, even the historically Red Tory-dominated Ontario PC party was already drifting to the right with the election of Harris as leader of the party. Jumping from the Common Sense Revolution to Western-rooted conservative populism was not that difficult.
The Liberals and the NDP, by contrast, have little in common. Both parties have roots stretching back well into Canadian history resulting in two very different institutional cultures. And although they have co-operated in the past, they’ve butted heads far more often (see, for example, Tommy Douglas’s famous “Mouseland” speech). There is a soft centre-left element to both parties’ support bases that do sometimes migrate between the two and do like to see the two parties co-operate. However, this element is outnumbered in both parties’ ranks by factions or interests that are frankly suspicious if not downright hostile to the other party. In fact, neither party has done particularly well when that soft centre-left element has been in control. On the provincial level, Bob Rae’s centre-left NDP alienated the labour and populist branches of the party (think Peter Kormos types), and it was precisely those elements of the party that distanced themselves from Rae that survived the coming decimation of the ONDP.
Besides that, many in the NDP are resentful that the Liberals have taken credit for their innovations (like universal healthcare), and many are frustrated with the Liberal strategy of campaigning to the left, but governing from the right. In some of their core areas of support (especially urban ridings), the NDP are also far more used to running against the Liberals than the Conservatives and bad blood does exist between the two at the local level. Further, in provinces across Canada, the Liberals have merged with the Conservatives against powerful provincial New Democrats (Saskatchewan, BC). Rarely have provincial Liberals and New Democrats co-operated to keep powerful Conservatives parties at bay (ex. Peterson in Ontario).
Were the Liberals and NDP to unite, we cannot assume that their bases would be all too thrilled about supporting this new party. The “Blue Grits” would probably jump ship to the Conservative party (just as many Red Tories jumped to the Liberals after the right united). In the NDP, you have a wide array of interest groups and party factions that would probably defect. For example, the radical leftists in the Socialist Caucus, the descendants of the NPI movement, their Labour and populist wings, etc. I would imagine, knowing that their power would be marginalized in a united left, them going off and starting their own party.
After all, the NDP owes its existence on the federal scene to the voices of dissent in another merger. When the Progressive Party and the Conservative Party “merged,” the majority of the Progressive Party migrated back to the Liberals. The more radical leftwing of the party broke off and formed the Ginger Group, eventually leading to the formation of the CCF, and later, the NDP. Democratic Socialists the world over have resisted when their big-tent parties move towards the centre. In Europe, they often form coalitions or alliances with Communist parties (ex. the German Die Linke). Even in the US you have guys like Bernie Sanders who don’t join the Democrats (though I believe he sits with their caucus in the Senate).