Hi brynmaes,
I don’t know a lot about the local market there but there are a few manufacturers or retail stores that are likely among your better choices. Of course as with any manufacturer or store you plan to visit … I would call them first (along the lines of this article) to find out their willingness to provide you with information about the materials in their mattress and to get a general sense of what to expect if you decide to go there. The manufacturers include (and all of these may not make latex but I’ve included them for reference) …
http://www.beambedding.ca/en/ Waterloo, ON Factory direct manufacturer. Makes a line of innerspring mattresses with high quality polyfoam and natural fibers but I don’t think they make latex or memory foam. A call would find out for sure.
http://www.waterloomattress.ca/ Waterloo, ON Factory direct manufacturer. Makes their own innerspring/polyfoam mattresses and also carries Tempurpedic (memory foam) and Natura (latex).
http://www.cjmulhollandmattress.ca/ Hamilton, ON Factory direct manufacturer. They make a range of innerspring and memory foam mattresses. They also carry latex but these may be Natura and not manufactured by them. Call to check.
http://www.newdawnmattress.com/ Hamilton, ON Makes a complete range of latex, memory foam, and innerspring mattresses with good value.
http://www.thefoamstore.ca/ Kitchener, ON. Makes and sells mattresses that use high quality polyfoam and memory foam and have some good value.
Furniture & Home Décor - Bring Home To Life - IKEA CA Burlington, ON. See post #3 here for some of the better value here.
The Toronto list in post #1 here also has some manufacturers and possibilities that may be within reasonable driving distance as well.
Some local retail outlets (from a quick scan and a couple of conversations) that may have some latex possibilities and the brands they carry that I would focus on (again making sure you call first to find out their ability and willingness to tell you all the layers and to get a general sense of their knowledge and service) include …
http://www.themattressdiscounter.com/ Burlington, ON Retail direct for Dreamstar. Have some latex hybrid mattresses (and other styles as well) on their floor and can also custom order.
http://www.sleep-ezzz.com/ Cambridge, ON. Dreameasy (see this post and make sure you receive the correct mattress).
http://www.furniturewonderland.ca/ Kitchener, ON. Galaxy Bedding.
http://www.premiumwholesale.ca/ Kitchener, ON. Dreamstar, Dreameasy
http://kitchenermattresses.com/ Kitchener, ON. Several local manufacturers.
http://www.paylessmattress.ca/ Guelph, ON. Dreamstar
http://www.parksfurniture.com/ Hamilton, St Catharines, Niagara Falls, ON. Galaxy, Springwall
Time permitting I’ll look a little further to see if there are any other latex choices more local to you but these should give you a starting point at least.
Phoenix