Is this a fair trade?

I would say yes. Brandon Lyon is a less than adequate Closer who will provide you with a few saves but run up your ERA and WHIP. Johnson is a good pitcher and Morneau will pick up his game as the season goes along, but here is the kicker: You are getting a good outfielder, which I am guessing you need, and you are clearing two more spaces on your roster to add players from the waiver. I am sure that you can find a few players on waivers that are as equally valuable as Lyon and maybe as good as Morneau.