Hi hmorneau,
There is a list in post #21 here of some retailers or manufacturers that ship across Canada that may be worth checking but I’m not sure which of them supply foundations or the cost involved for any of the US suppliers to ship a KD foundation to Canada (although I know that both mattresses.net and SleepEz carry good quality KD foundations that can be shipped through courier and ship to Canada).
Some other possibilities from a quick google search (or the foundation list) include …
http://www.bedcetera.com/scripts/prodList.asp?idCategory=570 has some slatted platform beds that they ship across Canada but I’m not sure of the specifics of the center support or the distance between the slats so you would need to check (assuming that a platform bed is something you would consider).
Ikea has some bedframe/slat options that should be suitable.
http://sleeptek.ca/products/classic-wood-slat-foundation These are good quality but I’m not sure of any shipping costs or whether there is a dealer near you.
http://m.sears.ca/product/natura-high-profile-foundation/601-000366229-279FH2 Also good quality but more costly
https://www.directshops.ca/categories/Bedroom/Bed-Frames/ Sell KD foundations but I’m not sure of the gap width and I would suspect it’s more than 3"
I’m not sure where you are but local stores or manufacturers that sell latex mattresses may also be a good source
Phoenix