New(ish) versions of LaTeX provide an enhanced NFSS (i.e. a New New Font Selection Scheme) which allow you to specify different default weights for typewriter, sans and/or roman.
changes the weight bold and regular series specifically for the typewriter family.
The following (typographically dubious) sample shows the result when Cascadia Code is used for typewriter, while the default Computer Modern is used for roman.
Moreover, this is produced using just the standard
\mdseries i.e. the regular Cascadia is used as bold typewriter and the light as regular, while the standard series are used for roman.
It is not possible to use Cascadia Code italics or oblique because these shapes are not available. So this answer fulfils your desiderata insofar as they are possible with
cascadia-code and fails to fulfil them insofar as they are not. If they were available, you would not need to do anything additional to enable them. The two lines above switch the weight used for regular/bold typewriter of all shapes - upright, italic, oblique, small-caps, italic small-caps, oblique small-caps, swash, upright italic .... It just so happens the only shape available with Cascadia Code is upright.