Check with your local garden centre to make sure, but I think you should be OK in northern Alberta if you

a) line the urns with plastic and newspaper before putting in soil and the cedars
b) slide the cedars out of the urn when the weather gets colder
c) heel the cedar root ball into deep soil to overwinter
d) wrap the branches in burlap to prevent dessication

In the spring, you'd dig them out of their heeled-in position and drop them back into the urns.