Heineman is easily more valuable than Evans right now.
Heineman's just turned 23 as a rookie, is fast, physical, big, good defensively, shoots well, reasonably-talented, and thinks the game well overall.
Then there's also the fact that Heineman's produced a lot of offense for not a lot of minutes and mostly defensive assignments on a bad team.
So yeah, if Heineman builds up on his performance this season next year and beyond, he could be a foundational type of piece on the bottom-6 for Montreal.
Jake Evans would be nice to re-sign too, but in the current market it might just be better for Montreal to trade him and try to replace him internally (Beck, Kapanen, and Xhekaj are showing extremely well in their respective leagues and could be good 3rd/4th liners in the future).
Oh, and Evans likely won't be traded for a 2nd-round pick.
The Canadiens already have multiple second-round picks in this year's draft and also next year's, so chances are high that they'd rather package Evans with additional picks/players to obtain a first-round pick in either the 2025 or 2026 drafts.
Basically, quality instead of just getting more quantity in the case of an eventual Evans trade.