As this is primarily an edible plant blog, I'm going to focus on plant mail-order houses with edible entries, but there are a list of nurseries in the area that may have what you're looking for or MAYBE will order them in. I say maybe because I've submitted various requests that were filed under 'not in our lifetime.'
This will NOT be a complete list 'cause I don't spend all day on the internet. Feel free to contribute your brain power and free time to the project by recommending others.
Mail-order Edible Plants in Canada:
Acorus Restoration: Native plants, many edible. Generally listed as mail-order
Alberta Nurseries: Hardy tart/sweet cherries and other small fruits. Not a huge selection.
Alcla Native Plants: Some edibles most notably ground plum - Astralgalus crassicarpus which I normally only see as seeds such as from Prairie Moon Nursery (US native seed and plant source)
Bamboo World: I have not researched which would be good to eat but if you have the right zone, then here's a source.
Beaver Pond Estates: Seed garlic - link takes you to seeds of diversity page for email
Boughen Nurseries: Fruit trees and plants including U of Saskatchewan Cherries and cultivars of Seabuckthorn.
Boundry Garlic - Lots 'o garlic.
Clear Sky Farm: Heritage Garlic Varieties.
Cornhill Nursery: Small fruits, including a good selection of grapes for mail-order.
Denman Island Heritage Apples: The name says it all, includes cider apples
Eagle Creek Farms: Lots of potatoes. Years ago, I ordered from them with very good results.
Fraiser Thimble Farms: Has some edible listings
Golden Acres Farm: Seed Garlic. No direct link to website so linked to Seeds of Diversity info
Golden Bough Nursery: Sells Red Mulberry, American Plum, grapes, some other rare fruits and nuts
Green Barn Nursery: Odd naming practices such as using the term apple-pear for an asian pear, and using the heading cranberry for high bush cranberries. Nursery stock is interesting but expensive: crosses between cherries and plums and a cross between an apricot and plum, mulberries, nuts and more.
Grimo Nut Nursery: All sorts of interesting things from paw-paw, quince, north hardy nuts to mulberries. My trees arrived in a good condition and grew well so far.
Hardy Fruit Trees: Doesn't the first picture make you wondering if he's peeing on his plants? At any rate, good selection.
Hawfield Farm Garlic: Garlic farms don't seem to like to have websites so I'm pretty sure this is the right one.
Henry Fields Seed & Nursery: Small berries, trees and some veggie starts
Heritage Harvest Seed: Perennial walking and potato onions.
Hortico: Fruit trees and plants along with lots of other perennials and woodies.
Humber Nursery - Fruit and Nut trees available - not clear if plants are shipped
La ferme tourne-sol: Jersusalem Artichoke and chuffa
Maddog Farm: Just discovered this one (Thanks Mike!) Large selection of Jerusalem Artichokes, potatoes and sweet potatoes. Also sells crosnes (Stachys affinis). Also sells honey bees.
Mapple Farms: My original source of sweet potatoes and crosnes. They also sell the Volga2 variety of Jerusalem Artichoke. Mr. Allan's plants have always grown well for me.
McFayden: Various small fruits and some fruit trees
Mr V's: Good selection of fruits including cherry-plums. Said to be expensive compared to others.
Mycopatch: Mushrooms - navigating this site is not easy.
Pine needle farm: Tree nursery
Rhora's Nut Farm: I've not ordered from them before but they offer some unusual nut and fruit trees that are hard to come by like cornelian cherry and beach plum. My only complaint is that they sell inoculant for their different plant categories.
Richters: Venerable herb house of Canada with lots of offerings including some fruit trees and vegetable starts. Prices are reasonable and though the size of the plants are small when they arrive, they grow well in my experience. Lots of seeds too.
Saskgarlic: You guessed it.
Seeds of Diversity: Last time I received their trade catalogue, there were cuttings available
Silver Creek Nursery: Reliance peach, asian pears and more
Siloam Orchards: These guys come up as a mail-order house though I couldn't discover how to order. Mostly apple varieties but also asian pears, cherries and more. They sell perry pears too which I have just discovered are pears selected for cider production.
Strawberry Time: Mostly strawberry and raspberries, good prices.
T&T Seeds: Interesting plant selection from hardy kiwis to Saskatoon berries.
The Cutting Veg: More garlic!
The Mushroom Patch: Large selection of kits and plugs. I can't tell you how my plugs did yet as they were started just last year.
William Dam Seeds: The usual: asparagus, raspberries, strawberries, potatoes and so on.
Some specialty or collector perennials, such as daylilies, are also edible but slogging through those numerous websites is making me woozy. For what it's worth, it's normally easier finding seeds of interesting species of popular edibles such as citron daylily and red-leafed dandelion.
Also, conservation societies can be a good place to get inexpensive tree seedlings for reforesting. Ferguson Forest Centre is nearby. Try native nurseries and sales too for plants such as edible fiddleheads.
* It was supposed to be definition day but I decided to do Part II next week as I have an eye on getting some more trees this week :)
** They also sell bloody dock, various shallots, garlic, walking onions, lovage, various hops, more mint than anyone should plant and lots and lots of herbs many of them with culinary uses.
Coming up next week:
Part II - Not all Seeds are created equal from hybrid, heirloom, landrace, GMO, species, GREXes and more.