Does the climate allow for a 38 game season up there? Even with summer football? Even with lots of scheduled games on midweeks?
Remember - you lose dates to internationals and FIFA/UEFA will demand several weeks every two years for the World Cup/Euro.
The Allsvenskan (or is it Superettan? I always get my Swedish divisions mixed up ...) plays a 30 game season today.
I'm not saying that a 20 team league cannot be done - but please look at available matchdays.
August to late May - 42 weeks or so (with no break)
Mid March to late November - 36 weeks
The Scandinavian leagues currently have around 16 teams each, so it's not unfeasible.