None. No amount of rearranging deck chairs will address the center position this season. It's nothing but grasping at straws.
Looking at the two players you suggest, there are a myriad of issues.
1. You're talking about $10.4 million in salary. I can't think of one team interesting in taking on that much cap and/or have a player they'd be willing to part with.
2. Remove Galchenyuk from the LW discussion for a moment. Montreal's left side is crowded. Pacioretty, Drouin, Lehkonen and Byron. Lehkonen is poised for a 20g season. Byron showed what he could do given a chance. I expect a dip, but he'll still be valuable. Neither player is a 4th line player. Pacioretty is a first line lw. Drouin is a #2 at least. So, you've got 4 guys for three spots. I think Max should move to the rw as he scores so much from that side. Even so, you're still full on the lw. That means Alex is back at center. Trade him and you're not 'adding' you're simply moving out one piece for another and still have Plekanec as your likely #2.
Best to ride out the season.