I'm not a fan of trading a young promising C like McCann and the 33rd overall pick for someone who is really more of a number 5 defenseman. I guess understanding how hockey analytics works means I have zero credibility though.
I'm not a huge fan of the trade, but I do understand the trade. It isn't easy to get young RH defensemen who can play in the top 4. Gudbranson is more of a #5D, but he's also 24 years with the potential to get a bit better and be a #3/4 guy in the next couple of years.
McCann potentially could have become a #1b centerman, but more likely he will top out as a #2C. So the trade shakes down like this...
Van gives up a prospect as follows:
40% chance #2C
5% chance #1C
55% chance fringe player (ie: Kyle Wellwood)
Van gets back a definite #5 defenseman with upside as follows:
5% chance to become top pairing
60% chance to get a bit better and become at least a solid #4D (he's 24, he MUST get a touch better as defensemen peak in their late 20s)
35% chance to just stay as a #5D
I had to make some guesses, but even if I'm a bit off with the percentages I think you get my point. Also for mid-tier players we received the player with the more valuable position.