Political party leaders should not be chosen based on the region of the country they come from. Obviously. It should be based on a number of other components, all revolving around fitness for the office.
However, having said that, there is an obvious political capital to consider regarding the issue 'where is the leader from' in a country as regionally fractured as Canada. Provinces, and more largely speaking regions (both sub-provincial and supraprovincial), tend to support 'favourite sons' - and the party they come from - in larger than average numbers. It's a factor that's difficult to measure (did Québec as a whole support Mulroney merely because of his Québécois birth or because of his promise to solve the constitutional standoff, and the beau risque?), but it's a factor that definitely exists. Parties are also clearly aware of it, since they seemingly never vote for leaders from the same region twice in succession.
So in consideration purely of strategy, where should the parties look when their current leaders resign?
When it comes to the NDP, there are two obvious answers. The first would be Québec, who has never had an NDP leader (Jack Layton is Montréal born-and-raised, but is very closely identified with Toronto). At present the NDP are performing as well as they ever have in Québec, but there's a sense that a glass ceiling exists there. The NDP has a very 'anglo' image, and a Québécois leader, particularly a francophone one, might change that.
Yet there is a risk here - a risk that a lot of traditional NDP supporters would see it as a further move east, a further move toward cities, and a further move away from the NDP's roots. A party can - and should - evolve, but a party shouldn't turn its back on its 'roots'. The past few years of Harper Conservative rule have affected Western voting trends in a number of strange ways, but the loss of NDP support in the West has been marked. Perhaps it's just because another party has a favourite son, and post-Harper Western votes might naturally return to the NDP. But amazingly the NDP has not had a Western leader since Tommy Douglas. It's actually mostly been Ontario since then: Ontario, Ontario, the Yukon, Nova Scotia, Ontario. Another firebrand Prairie populist might rejuvenate the party, but it also might undo decades of advancement outside the Prairies. It's tough to tell. Someone from Vancouver might be a shrewd compromise: Western, but urban.
When it comes to the Liberals, one thing immediately comes to mind: not Ontario (sorry Bob Rae). Not just merely because Ignatieff is 'from Ontario' (inasmuch as he's from anywhere in Canada at all) but because the Liberal Party has a pretty weak tradition regarding Ontario leaders. Its best leaders have inevitably come from outside Ontario.
In fact, they've come from Québec. The Liberal Party has a long-standing tradition of alternating Ontario and Québec leaders, at the expense of the rest of the country. Westerners are well aware of that, and it's one main reason behind the underlying view in the West of the Liberals as an 'eastern' party. But if both Ontario and Québec have been sending up squibs lately, might it not be time to try elsewhere? Probably. The West or the East? I'm not sure, really. The Maritimes have been pretty faithful Liberal supporters for a while now - ever since Robert Stanfield, come to think of it, the Maritimes' last great favourite son (a PC). Often in consideration of political voting blocs, the Atlantic Provinces are unfairly overlooked behind the three larger blocks of West, Ontario and Québec (the North, with its three seats, obviously suffers the same fate, which is why it's odd that the only non-Ontario NDP leaders of the past forty years have come from these two regions), so it might make sense to go for a Western Liberal leader. Except that that feels almost like an oxymoron somehow, and runs the risk of pretty much eliminating the Liberal brand within the province of Québec. It might be interesting to consider an Atlantic Liberal leader: it could ne a non-controversial reboot for the party, one that could cement its eastern lead while not affecting its standing in the rest of the country that much (Québec has little except hockey in common with the Atlantic, but Ontarians view the East as largely an extention of Ontario anyway).
What about the Conservatives? Hated by many as he is, I would hazard a guess that the Conservative Party dreads the day Stephen Harper resigns. The 'unity' that Harper has quite successfully established within his party has served to obscure memories of the 90s, when members of the Conservative Party's two predecessors were actually quite hostile to each other. But the common branding hides the fact that divisions still exist between former PCs and former Reformists. And that is, as much as a political distinction, a regional one. Toronto-born-and-raised Harper is very much identified as a Westerner, to the point that his Ontario upbringing is really no more relevant than Layton's Québec upbringing (or Elizabeth May's American upbringing). So the traditional Canadian logic would be 'have the next leader not be from the West' - and there's a lot of talk about the political capital of perhaps electing a Québécois leader next. Possibly - but the risk there is of massive alienation, possibly to the extent of a second fracture, by the Reformist loyalists who have given the CPC much of its infrastructure. Not (entirely) due to animosity toward the Québécois but also due to the fact that the CPC in Québec is the descendent of the PCs, not of Reform. Whatever happens post-Harper, the previous party differences will return, and I'm sure there will be a sense among 'red Tories' that it's their turn to shine. The only parts of Canada that can lay a realistic claim to representing both the Reform and the PC traditions are (a) New Brunswick and (b) Ontario, outside of the GTA (some urban centres in the West might be able to make this claim too). If the party comes to see this as an important criterion, then they should look to Ontario.Otherwise, maybe they should bite the bullet and elect a Québécois, one with excellent English who can rebuild the remarkable coalition Mulroney built. This isn't possible under Harper, but under a successor? Well, all bets are off.
Elizabeth May is a one-person microcosm of English-speaking Canada anyway, somehow being a Nova Scotian and a British Columbian at the same time, while also having run for office in Ontario. Jim Harris was from Ontario, so the obvious choice would be a Parti vert member from Québec. But I don't know who that could possibly be.
Oh, and speaking of Québec, once Gilles Duceppe leaves the BQ for the PQ, the Bloc should... er, look to Nunavut for a new leader. That's what they should do.