Next year

Severson is too old for the Canucks window at this point

Too old? Perhaps you mean the term on his contract (1.5 years) is too short.
(which makes sense).

Both but I was referring to his age. Doesn't make sense to acquire anyone older than Garland with how the team is playing currently

If Vancouver were my team, I'd probably be looking at it the same way.
Build a new core around Petterson (23), Hughes (22) and Boeser (24).
Move out Miller, Horvat this year for maximum return...ideally get back one young future 3C and one young defensive RD.
Than try to get future 2C...and a couple d-men in next two drafts.

Yup pretty much my exact thinking. Only way I'd move Boeser is if he's not willing to sign a long term deal