

Hardy pecan seedlings
Pecans in southern Ontario? Yes! Like any nut tree they take a while to start producing - don't expect nuts any sooner than a decade - but that's the beauty of nut trees; you're growing food for future generations of humans and other animals.
The pecan nuts themselves are smaller than the pecans you're used to from a grocery store, but they have all the flavour. They're delicious, and easy to crack.
MY pecan trees are one year old, and are between 12"-16". The advantage of planting young, small trees is that they transplant and establish themselves well.
My seed source is Grimo Nut Nursery's orchard in the Niagara area. I have two hardy pecans in my yard, and in my case, after 12 years, they are about 15' tall, and one has begun flowering.
Pollination: Like most nut trees, pecans are wind-pollinated and require cross-pollination with another of their same species in order to make nuts. With pecans it's good to have three trees, or more, to ensure the best chances at compatible flowering times among the trees.
Thinking long-term, another reason to plant more is that if you ever want to save seeds from your own population of pecan trees, more trees equals more genetic variation among your seedlings, which means a more robust population. An isolated population is a genetic bottleneck that reduces the variation of the population's genepool, which will not bode as well for the next generation of seedlings.
References:
Society of Ontario Nut Growers article on the northern pecan.
Grimo Nut Nursery's hardy pecan cultivars.
Image 1: Andrey Zharkikh.
Image 2: Grimo Nuts.