I think it's always a great idea to attempt propagating trees from seeds, but you do face a number of challenges with your chosen tree. First, southern Manitoba is in the DED infection zone, and you're going to always run the risk of losing your trees. You could try to grow U. rubra instead of U. Americana, as it's reported to be somewhat more resistant to DED, but you should probably expect to have your trees ultimately be infected with it.
Second, U. Americana seeds can have very low levels of viability -- I think that one study from Ontario suggested that only 1-2% of seeds are viable! Be prepared to sow a lot of seeds in order to get a few seedlings. Elm seeds also tend to decay rather quickly after they're produced, so you should try to plant seeds from this year's crop. And try not to pick seeds from areas that may have flooded.
Finally, you might want to consider planting the very-underappreciated and somewhat related hackberry (C. Occidentalis) instead of an elm. They're similar in form to the American elm and have edible fruit, too! Hackberries are native to southern Manitoba, so you're likely to find them at a local nursery.

Well, when I say poor, Im at about 30-50% of seeds sprouting, so not *too* bad at all compared to you 1-2%, especialy since I'm using seed I collected last year and put in the freezer.
We have a few test trees around here that are innoculated with the anti-virus for DED, so I try to gather from those trees when they seed.

Ive never heard of hackberry, so I'll do some research on it, but I do love the look of elms.

If these DED resistant elms you speak of are the known resistant varieties (valley forge, princeton, etc) you should be better off against DED but not completely. You may still have infections. Sow the seeds right when you collect them, or would collect them if they are from last year. This is how the tree would propagate so you can trust mother natures timing.

If you have some extra seeds collected recently I would love to have some or trade you something for them. I can send a SASE but I'm interested in doing Am. Elm starts myself.