For example, the Stars and the Caps for this year.
This is modern era, where we've had full 4-tier playoffs.
Yes. The NHL spent 25 years with only six teams (the "Original Six" era), and to some extent only three of those teams were competitive, so this has happened many times.
Going even further back (to the 1920s), the playoffs were just a matchup between the top two teams, so this was guaranteed to happen.