Attribution rules do apply to cash just as much as they do to non cash assets.  The difference in most cases is that cash unlike most other assets often has a much less clear paper trail.  Which essentially brings up the issue of materiality.  A gift of $1,000 is unlikely to draw the attention of anyone.  However, if you give your spouse who earns $20K a year a gift of $20K and they deposit it for the purposes of earning investment income you can be certain that the chances someone at the CRA will at least take a second look at it will raise significantly.

The best way around this is to ensure that the lower income spouse doesn't pay any household bills meaning that they are free to invest all of their income.