I'll play!
I think that you're giving up too much.
I also think that a 2nd and a B prospect won't do it. There are more than one team interested in Markstrom and that will drive the price up a little.
If you retain 50% on Markstrom, that's worth a 29 pick OA according to PuckPedia's calculator.
So the difference in value between 10 OA and 29 is 17 OA, again according to PuckPedia.
So to make it a fair trade with NJ, you have to get Markstrom for around 17 OA value.
I think that's acceptable value for him at full salary considering the demand around the league, even if he's a bit old.
The average value for Calgary's 2025 1st happens to be 18 OA, considering that it can turn out to be a high as 11 OA and as low as 32.
That part is debatable but i'm sure that Calgary would like to have their pick back and not have that hang over their heads for the duration of next season.
The Habs could add a guy like Harris, who the Flames were rumored to be interested in, for a 2nd.
So my proposal would be:
To Calgary:
Their own 2025 1st
Jordan Harris
To NJ:
Markstrom (50% retained by MTL)
To MTL:
2024 10th OA
2nd from Calgary
It can be tweaked a little, but i think it's in the ballpark.
Also i'm not sure that Markstrom has to be retained on. Retention can be substituted with 26 OA to NJ.