The answer is a definite "no". Even though sales volumes do decrease in the non-prime selling months (e.g. Nov - Jan), sale prices march in only one direction - up - regardless of the season. So waiting for a dreary day in mid-November to put in an offer on a home in hopes of catching a bargain is not a sound strategy. There are simply too many buyers waiting in the wings, at all times of the year.
But there is strategy involved when it comes to timing your purchase: the quality and depth of listings improves by leaps and bounds in the prime months of March to May and September / October. Yes, you will be competing with more buyers in these months, but at the same time there are a LOT more quality listings to choose from.
This fact is especially important if you have a very definite set of 'must-haves' on your list (e.g. "the backyard has to face south AND be completely private), or your geographic range is very specific (e.g. "I want to live within a block of Trinity Bellwoods Park"), or you want to purchase in one specific condo building. In the slower months of the year, weeks can go by with very few of what I'd call 'quality' listings coming up, i.e. homes that are well maintained and on the most coveted streets in the neighbourhood (or in the case of condos, units with prime views and on higher floors).
Bottom line: holding out for a bargain deal to come along in the slower months - not at all based on reality.
But understanding that in the prime selling months you have your best shot at finding your dream home, and being ready to act within hours of a new (perfect for you) listing being posted - this is the key factor when it comes to timing the market.