The husband and I frequently chat about this very topic. We have "imaginary lived" in many different places over the past few years.
Our general criteria is as yours, walk able, good transit, reasonable housing prices etc. (yada yada yada) It would be nice to have better winter weather, but we could compromise by heading down south instead :)
I have to also entertain a place that has access to the water for the husband's sailing adventures - which could / would include a reasonably priced yacht club & racing.
As much as I love the Maritimes for their reasonable house prices (I am from there), travel by car is inevitable, food can be more expensive, access to health care is predominately in the Metro Halifax area. Also Income taxes for lower incomes are considerably higher than in Ontario & BC. Oh, and don't forget the ridiculous HST there.
So - It is either Ontario or BC for us, for low taxation on low incomes, and they also have favourable taxation on dividends with low incomes.
The current city on the list is Brockville, Ontario. (just east from Kingston & Gananoque). Right on the main highway, near the 416 to go to Ottawa.
It has a hospital, very good transit, a community college, Wal-Mart, and other Big Boxes within 5-6KM of the downtown core. Very reasonable houses (bungalows around $150K, some places cheaper, newer homes higher).
Although it is about an hour away from the Ottawa Airport, it is very close to Ogdensburg, NY which is selling itself as a airpoint access point for us Eastern Ontario people.
What I find most interesting is that it is on the spur / split line for Via Rail on the corridor. One train to either Toronto, Ottawa, or Montreal. I see faster, and more commuter rail coming for the future - so this could be very good.
It has a long standing farmers market too.
There is a funny side to it as well, because it is a smaller city town, the local paper is filled with anything that is "news". Some of it quite unusual. Certainly things that would never make to the front page in a larger city. Personally I find this amusing.
I'm very interested in other locations too!