1st, I'd suggest you skip over to the tree forum and pose this question as there are many 'experts' over there. I'm somewhat familiar with the juglone problem but only from what I've read.

I will say however that if you want trees that don't need pampering then I'd go for trees that are native to your area. They adapt much better.

I've never had the pleasure of visiting Ontario...tho I hope to someday. I don't know what's native to your region but I did find a link that may be of help to you. I took a peek and you have many wonderful trees to choose from.

Here is a link that might be useful: Native tree's of Canada

I did a search on "trees affected by juglone" and go lots of hits. I've posted one below but you might wanna do a search for other info.

Here is a link that might be useful: More

hackberries often grow with walnuts in floodplain soils (infact, the're cohorts on their favorite soil) so knowing that id assume that there not strongly effected by juglone; however, hackberries are also strongly alleopathic but i dont beleive they affect walnuts either

Walter Reeves's website has an article on alleopathy and lists many plants that will (and will not grow) around Black Walnuts.

Here is a link that might be useful: Walter Reeves on alleopathy

I have three black walnuts in my woodland area and I have found out that azaelas don't work for me there. However, you asked about trees: and there are chokecherry trees growing nicely in this area, don't seem to be bothered by the walnuts.

I believe Japanese Maples, Redbuds and River Birches are compatable. Also, I have many, many White and Norway Spruce growing in close proximity to Black Walnuts.

I have Black Walnut trees on my property also, the other trees I have are mostly Norway Maples,and a couple of Ash Trees, these trees are quite old and don't seem to be bothered by the juglone from the Walnut Trees. I do know there are many others that will grow with them, good luck in your search!
Holly

I have sassafras and tulip trees growing in abundance near my black walnut trees (and near everything else). However, both sassafras and tulip trees have very brittle wood even when mature so I would not reccommend them for near any structure or where you park the car. I have some azaleas and rhodos growing well at just about the drip line of a mature black walnut. They have been there about three years and so far so good. Under the canopy of the walnut I have some elderberry volunteers and jewel weed and a little further past the drip line I have some volunteer heath aster (I think it's Heath Aster, looks like the picture in my book anyway).
MamaHolly, in my experience not much of anything bothers Norway Maples - I have even had trouble killing them off.

bob64 - oooh I would love to have tulip trees. They are so cool. I have a little yellow magnolia whose flowers remind of the tulip tree's flowers.

The funny thing is I met this guy who is SO freaked out about the idea of juglone that he practically sterilizes himself after leaving my yard, lest he kill all the plants at his place, because he was NEAR black walnuts. Made me put things in perspective. I have decided not to worry about it. I have daffodils and tulips and lilies growing under the drip line and they have come back for 6+ years. I have all kinds of beds that I built right near the trees (albeit with trucked in soil) that get the shade and the leaves fall on them, etc. and the plants (perennials and bulbs) are all fine. I have decided to plant most of my trees some distance away because of the shade factor - those walnuts have pretty dense shade.

Bob,
Yeah Norway Maples are kind of like weeds, not my favorite,but they were here when i moved in. One thing I forgot to mention, well, 2....I planted some bamboo near my one Walnut, I didnt think it would do very well but is growing fine, what a surprise, I also did a search titled planting under, near Black Walnut trees, came up with some good hits, one from the Univ. of Ohio has a list of all kinds of plants that will grow, I printed it to take with me to the Nursery.
Mama

I have dogwoods and hemlock and spruce and yew near my black walnuts. Pines grew well but seemed to have a shorter life.

Cnid,
I read on Wickipedia that Tulip Trees grow in Southern Ontario. Is that close enough for you to try?