The swiss U20 national Team played 2-2 against the U.S. team some years ago at the WJC and they are losing against teams from the minor league of the highest one in Switzerland... That says everything.
Canada's Spengler Cup team would easily beat Canada's World Junior team. They played a close game against a team from the KHL, who would kill any junior team if they were matched up. I have no doubt the Spengler Cup team could handily beat the CIS teams that the juniors routinely lose to.
The Spengler Cup team would probably win. Let's not forget some of the players on that team were once upon a time sparkling NHL prospects, and also, on any given WJC team, there will be a number of NHL busts who probably won't be good enough for a Spengler Cup tournament when they're older.