I beg to differ...

Usually it's the most restrictive fare rules apply.

So if the lower fare does not allow a stopover, then you aren't allowed a stopover even if the higher fare allows it. If the most restricted fare permits a mnimum stay of 7 days, then the 7 days apply.

The airline themselves of course may override the rules and allow you the more flexible of the two. But then we are talking about Air Canada here right?