In Ontario, the choices for buying wine are either the LCBO (Liquor Control Board of Ontario) are at the winery itself. Since wine is not sold through retail stores, the Toronto choices are LCBO stores. The ones that specialize in deep collections of wines are called Vintages stores. They have a strong online presence at http://vintages.com . (You can also trust their reviews, pretty much, because as a government agency, they don't have much of an agenda to favouring one wine over another, other than their reputation). A piece of trivia: the LCBO is the world's largest buyer of Bordeaux!
I usually go to the Cooper Street store (i.e. Queen's Quay, around Jarvis), which is the flagship. Actually, the "new" flagship may be the store at Yonge and Summerhill, which was recently renovated after being a long-neglected unused train station.
You can check online reviews of new releases at http://www.winereviews.ca/ or http://www.gangofpour.com/kerr/index.html . (The search at http://www.wineaccess.ca used to be the best, but now they charge for it!
On the trip to Niagara, if you can only stop at one place, it probably needs to be the Jackson-Triggs Winery http://www.jacksontriggswinery.com/, which is very interesting architecturally. Thirty years ago, when I first started touring Niagara, the "must" stop was Inniskillin, http://www.inniskillin.com, where I haven't been, recently. (I believe that they now charge for tastings). Last year, I stopped by Hillebrand http://www.hillebrand.com -- nice tour, but the wines weren't very impressive. (Standards go up when you're on the wine route!) There's an extensive site at http://www.wineroute.com , and the maps are available at any winery, or from the tourist offices.
I don't drink a lot of icewine, but notice that brands seem to turn over quite often. $20Cdn for a 375ml bottle would be on the lower end the scale, so your selection may not be that great. If you're doing more web research, you'll find that there a different grape varieties (i.e. Vidal) such that there is quite a range of flavours.
My favourite LCBO outlet is the newly renovated Yonge & Summerhill location. Best selection! I have only been to a few Niagara Wineries, but the one that most impressed me was Malivoire, on the Beamsville Bench. Wonderful wine and an interesting gravity setup. No restaurant, but there are a number of other wineries very close by. I could be wrong, but I don't think you can get an ice wine for under $20. Late harvest wines, perhaps...