My answer would be: nothing.
Right now, the Bank of Canada is doing the grunt work of trying to keep financial markets from drying up, and there's not a lot that governments can do to help. And if the Bank were trying to provide monetary stimulus on top of all that, it could hardly do better than the 15% devaluation that the forex market has provided.
If the federal and provincial governments do nothing, there's a good chance that they'll run a deficit, either this year, next year or both. And that's okay: we've spent the better part of a generation getting our fiscal house in order – we can handle it.
If Canada does go into recession (let's all remember that available data indicates that we were not in recession as of September), then we should not exclude the possibility of fiscal measures beyond the automatic stabilisers. But we're not there yet.
Update: Gilbert Lavoie puts it well in this morning's Le Soleil:
L'opposition demande un «plan». Qu'on lui en donne un. Ça coûtera
quelques heures de travail aux fonctionnaires, et le papier sur lequel
il sera rédigé. Quant aux fonds publics, attendons la tempête avant de
savoir s'il faut s'acheter des parapluies ou des habits de neige.
My translation:
The opposition wants a 'plan'. So give them one. It'll cost a couple of hours of a bureaucrat's time and the paper on which it's written. But when it comes to public money, let's wait for the storm to hit before deciding whether we need to buy umbrellas or snowsuits.
Worthwhile Canadian Initiative 
My answer would be: nothing.
Tell that to Brad Wall. He’s on a one man mission to rack up a huge deficit in Saskatchewan.
That would be Gilbert Lavoie, dear.
Fixed.
At least I got his last name right…
That was an exchange of assets: mortgages for CMHC paper. If we assume that the interest rate differentials cancel out default risks (and no-one seems to think that the mortgages are toxic waste), there’s no effect on the federal debt. A fiscal stimulus would increase the debt.
The CMHC bought the mortgages with corporate paper – IOUs, basically. Anyone can issue IOUs; the tricky bit is getting people to accept them as payment for other assets. CMHC paper is backed by the feds, so it’s relatively easier to get people to accept them.
This sort of intervention amounts to what the Bank has been doing for months: exchanging more liquid assets for less liquid assets. Finance is playing a supporting role for the Bank here.
Cost GHGs.
The “liquidity trap” is when monetary policymakers can’t cut lending rates anymore because they are near 0%, and printing cash doesn’t work because banks are too panicked to lend to eachother (whatever that means). Fixing the latter would involve either bypassing big banks by creating a Crown bank to lend to little ones directly, or to subsidize inter bank lending, say, with a volume-based tax-break. But IDK if the latter goals are good.
The IMF and World Bank are free market anarchisms devoted blindly to enforcing free market prescriptions rather than suggested alternatives of employment or poverty reduction. It appears some developed nations might be headed for the same type of market failures. Back during the Cold War it may have made sense to press for free markets beyond the point where public spending is more efficint than private. But now we need to reform IMF/WB to focus on maximizing the employable person-yrs of the developing world. With that prescription, we’ll find the solutions to our own economic troubles.
Hint: corporate tax and GST cuts for the rich and debt piled on boomer’s children are not the most efficient solutions despite being the free market prescription. Right now our gini ratio has just fallen below the OECD average and our child poverty rate is rising fast (translation: more rich Canadians will be murdered soon). We have just elected a government for the rich at a time when ROI of spending on the poor is at an all time high. Ethical traders should short BCE and Canwest, and (publicly funded) Ontario Teacher’s Pension should dump BCE and pickup Torstar.