I think Colorado have to add little bit more to match this trade
Prospect A- or B+ , maybe a second choice

Yeah I’d do this. I think Colorado might as well.

I'd do it without the retention. Colorado would return Annunen to the minors, so they'd have the cap space.

I understand that the value might not be there for Colorado, but I don't see why we'd take a horrible contract (Johansen), let go of a reliable (and polyvalent) 4C, and burn a retention slot for 2 years for a sole, late 1rst rounder. We have plenty of draft capital as it is.

I can get the fact that Colorado wanted backup experience to support there goaltender but what is valuable for them here ?

Johansson don't work as he should be (2c) and Evans would probably be doing the same job at cheaper deal but not sure that is interesting for them. If Monahan was not trade to Jets I would have say that an trade for him swap would be better.

Monahan 50% and Allen to get Johansson + first round pick.

Colorado would have received better center and get there backup they want and for Montreal you turn the third goalie problem into an center equilibrium ( -1 center and + 1 center) in the roster. Evans would still be your third Center and you add Gignac as your fourth one. This way there less stressed on both Suzuki/Evans.