This would depend on large part on:
*The terms of secession, particularly:
(1) whether independent Quebec takes on a share of Canada's public debt based on a pro-rata split, value of Federal assets within Quebec, etc., and
(2) Whether the new Quebec had to give up any territory, particularly any resource-rich areas of the North, Anglophone areas of Montreal (which, in turn, might not be economically viable outside Quebec), or the Hull region, where polls have suggested that the residents might choose to split from Quebec and remain within Canada, in no small part due to Federal employment. Chretien said, to broad agreement outside Quebec, that "if Canada is divisible, then Quebec is divisable," particulary the First Nations lands, which were not part of pre-British Quebec. If the First Nations voted to remain in Canada (as polls suggest most of them would), Canada would be obliged to enforce their rights.
* Whether or not the new Quebec became part of NAFTA
* Whether or not the new Quebec retained the Canadian dollar, or instituted their own, potentially less stable, currency.
One of the reasons support for independence has softened since the last referendum is that the position of the rest of Canada has hardened on these issues - in the run-up to that vote, the "soverignist" forces made it sound as if an independent Quebec would automatically accede to NAFTA, would be able to use the Canadian dollar, would take on no additional debt...hell, they even said Quebecois would retain Canadian passports. (Of course, they weren't being entirely honest on whether they were going to declare independence , but that's another story.) Well, all three existing members of NAFTA have to agree to new members, and there's no provision for seceded areas of existing members to automatically be in - and, if for no other reason than pure spite, Canada might block Quebec's entry.
There's a lot of variables here, and it's impossible to say how well an independent Quebec would fare. I would hazard a guess that, in the long run, it would be viable in the sense that its citizens would have an economy that affords them a decent standard of living. In the short run, there could be a lot of economic dislocation, especially if Canada blocked their entry into NAFTA.
I do think a truly independent Scotland - independent of both the UK and the EU - would be a poor country. And since the SNP is very pro-EU, I think it's safe to conclude they agree. My fear is that an "independent" Scotland within the EU would not fare much better, in that it would have to adopt the euro (no flexibility of interest rates), and without transfer payments from the rest of the UK would have to have either very high taxes or a sudden, wrenching adjustment to a lower-service government.