Good question, and one I have often wondered myself. I am always pondering these types of things...could this team beat that one? What would the score be, etc.
Considering many ECHL and AHL players are guys just out of junior or college (and therefore similar in age), and many of the Canada juniors could likely play for ECHL or AHL teams right now, I would say thay could compete, simply because they are the best 18 and 19 year olds in Canada.
Plus, when you think of it, a lot of guys in the minors are ones that will never see NHL ice or are late round draft choices, whereas many of the juniors will become NHLers and are first rounders.
With that said, the jump from playing against teenagers to playing against guys over 20 is not a simple one. Most AHL teams have some pretty grizzled veterans.
I would say against ECHL competition they would win more games than not, and against the AHL competition they would be in tough, losing more than they would win.