Weber will not be hard to move. There are enough GMs who'll think win-now, Team Canada vet, etc, etc. Look at Oshie signing an 8 year deal with WSH at a similar age, there are clearly GMs who are in win-now mode and possibly looking forward to the possibility of compliance buyouts. Weber at a 7.8M cap hit as a reliable top 2 RD would be marketable enough. Would Montreal get enough in return to make up for the fact that they offloaded Subban to get Weber....probably not. Probably not even close. But I think he'd be movable.
Not to mention, all his cap recapture years are done, so a team acquiring him could comfortable buy him out with a regular buyout 4-5 years down the line if he regressed. Never the less, most GMs don't think long term enough to be all that afraid of the Weber contract if it means being able to buy low on the type of player Weber is perceived as. Top 2RDs don't grow on trees.
Price is a wild card. He has a limited NTC, and he presents a major commitment. I genuinely don't know if he'd be tradable. I'd like to think he would be, but there are so few teams who'll be on his list who can fit him in, at that point MTL would be trading him just to move on and get something. Unless everything went perfectly, they certainly wouldn't get full value because the market would probably be very slim.