elenaleonova
Question: I live in Saskatoon (Zone 4) and I'd like a plant to act as a screen between my front and back yards. The wind comes from the northwest, has morning and late afternoon sun."
Answer: Screening plants are always tricky: they cannot be too dense, so you aren't obstructing the light, but just filtered enough to keep out an ugly sight. For this situation you have to take into account just how thick the foliage should be so you aren't intrusive as well.
Here's what I'd suggest: Salix salicola 'Polar Bear Willow', which grows to 4 metres high and 2.2 m wide at maturity. It will cope with both sun and shade. If that's too silvery, try the more traditional native, Amelanchier alnifolia 'Saskatoon Berry', which is a bird magnet, provides food and is glorious in spring bloom (5 m); or the Lonicera tatarica 'Tatarian Honeysuckle', which is first to leaf out in spring, grows to 3 m and is very bushy.