In the interim
Sadly, we find ourselves with only 34 candidates for the job, so it's actually fairly simple to write a short list.
For starters, no party's interim leader should ever be running to be permanent leader, except in extraordinary circumstances, such as war, disaster, or the national executive wanting Michael Ignatieff in charge. The reasons for this should be self evident, and Rob Silver spells them out here. I'd also add that any hint the "party elites" giving an unfair advantage to a chosen candidate would not exactly be in the spirit of engaging and unifying the membership.
So that likely means LeBlanc and Trudeau will take a pass, while they consider their options.
It's been argued the interim leader should be bilingual. Now, there are degrees of bilingualism, but I generally agree with this sentiment. Ralph Goodale would likely be the best candidate if not for ce petit problème. Similarly, picking Wayne Easter would have been a nice thank you to PEI, which now makes up 9% of the Liberal caucus, but he's a one language man himself.
Even with just those two small criteria, the field narrows considerably. Such are the problems of losing over half your MPs. From what I gather, the top contenders for the job are:
Stephane Dion: He's not being seriously considered, but I include his name here since someone will surely mention him in the comments section. Going to Dion would be somewhat fitting, but we all know the caucus, party, and country would never go for it. At the very least, we need to make the Tories produce some new attack ads.
Scott Brison: Brison is young, charismatic, and knows how to deliver a sound byte. Of course, for those very reasons, he may still be mulling over a run for the top job.
Marc Garneau: He may not be as seasoned politically as the other candidates, but he has name recognition. On the downside, if you think spending time outside the country is bad, just imagine what the Tories will have to say about Garneau spending time outside the planet.
David McGuinty: Would be a strong candidate, but his last name certainly complicates things with an Ontario provincial election on deck.
John McCallum: Somewhat more experienced for the job than the others, by virtue of having been named interim Liberal leader in 2008 by CTV.
Frank McKenna: Yes, I know he doesn't have a seat. But still, wouldn't he be a great selection!
The above would all make fine leaders, and lesser known MPs like Geoff Regan, Kirsty Duncan, or Joyce Murray also deserve consideration. And hey, there's always Jimmy K, though it would mean an end to his leadership aspirations.
But, above all these names, the one that stands out is Bob Rae. Rae is experienced, respected, bilingual, and well spoken. He would keep the Liberals in the headlines and would keep them relevant. It's hard to imagine a better candidate for the job.
Of course, for those reasons, Rae might very well decide to run for the top job. However, he'll be 66 by the time the next election rolls around, and my read of the landscape is that the Liberal membership is looking towards the next generation and a long-term rebuilt. I'm certainly in no position to tell Bob Rae he can't run for leader, and he would make a fine candidate. But a year or two as the interim leader would be an exciting challenge for a man who has accomplished so much over his career.
So it seems very much like a win-win. The caveat I'd place on it is that Rae must recognize this is a caretaker position. So that means no talk of leadership and no talk of merger.
But if he's willing to play ball under those conditions, I can't think of a better candidate for the job.