Canadian Politics Today

Generally speaking:

Foreign income should be earned in RRSP's so that no foreign withholding tax is withheld (assuming tax treaty in place which is usually the case). 

Interest bearing in RRSP's and TFSA's since it would be taxed at full tax rates anyway.

Eligible dividends ( dividends from most public CDN companies) ideally are earned in non-reg accounts (but depends...).

Cap gains earned in non-reg accounts too since inclusion rate is only 50%.

But all of that assumes a person is paying tax at high marginal tax rates, has fully loaded RRSP's and TFSA's, and still has excess savings to invest in non-reg accounts.

And the person wants to invest in interest bearing and/or Cdn dividend investments.

So we are talking about 5% or so of the population, if that.