I agree with what others are saying. But here's a little bit more info we could use that might help with a decision: how many kms do you drive in a year?
With high enough kms, you really do need 2 sets of tires, and if you keep the car for a while, costs end up not really being any different than owning just one year round set.
With low km driving, I can see the rationale for 1 set. The Nokian WR is essentially a marketing spin on an H-rated tire, where the winter performance is decent, and the wear on the rubber during the summer is at an acceptable level. You will pay a huge premium on these tires, as they pretty much dominate the "all-weather" category (I believe Yokohama may have introduced one, but I haven't heard a thing about it since it's debut), they are THE name in winter tires, and Kal-Tire is the exclusive distributor. You could achieve similar results with one winter tire that comes to mind - the Hankook Ice Bear WS300. For year-round use, I only recommend it if you do low kms each year and drive primarily only in the city.
There are a few posters on here who are adament against winter tire use in the summer. However as many others have pointed out, the drawbacks of a winter tire in the summer are far less serious than the drawbacks of an all-season or summer tire in the winter.