He's not the strongest, but I recall reading that Letang bench presses 400 lbs? He does have a solid frame.
I would probably go with someone like Doug Murray though. Guy is a beast.
Not going to say that's impossible (I don't know one way or the other) but that seems highly unlikely with a guy like Letang. He strikes me as more of a lean upper body with strong legs. I have doubts that he can bench double his body weight.
For pure max bench in the league, it's probably going to be a heavy guy like Dustin Byfuglien. Overall strength, probably Chara just because he's that big without a lot of body fat (lean muscle). Doubt his bench press is tops in the league, though, because of the length of his arms.
One of my friend used to run the strength and conditioning portion of training camp for the Edmonton Oilers and later the St.Louis Blues.
Back then Todd Marchant had by far the greatest leg strength (Completely off the charts-freakish levels of strength). His quads were tree trunks, but his Upper body was so skinny they should belong to a 12 year old.
Lubomir Visnovski could bench well over 400 lbs.
What I'm getting at is 'Strongest' is a really open word for this.
The person who benches the most, is likely different than the player who can squat the most, or military press the most.
Just like the guy that has the most explosive stride, might not be the same guy that can kick the hardest, or reverse leg curl the most.
If the question is more along the lines of: Which NHL player would win the 'Strongman Contest', my money is on Big Buff. He has the build of a 'Strongman' competitor.