I usually get them from blick, but idk if they'll ship to Canada... You can get the most inexpensive canvas (studio canvas) 11x14 from
here for 3.84 each, which is about $24-32 before shipping costs (if you get it shipped). I've worked at 3 different art companies for about 3.5 years and $3.84 is going to your best value unless you either 1. Stake out Craigslist or yard sales and pray to god someone has 8 canvases the same size they desperately need to get rid of, or 2. Forgo canvas all together and do your art on something non traditional like found wood panels or maybe cardboard.
as for the command strips: it depends on the canvas. If you get a small thin canvas, it could be fine, but if you're looking at museum depth canvases, it probably won't work at all. I recommend clear thumbtacks or even small nails.
--- Update From New Post Merge ---
For shits and giggles I looked on eBay and found artist's loft
http://m.ebay.com/itm/181369909345?nav=SEARCH which is a brand they sell at micheal's. unless micheal's is having a sale, I doubt you'll really find much lower than this. I use this brand in many of my painting commissions and its good with acrylics and stuff but like the blick studio brand, this is as low-quality-and-still-functional as it comes usually.