My package has been at customs clearance for 6 days - is this normal?

More than likely. I sent a girl I know in Colombia a package of prenatal vitamins and something that was supposed to help her nausea. She was 2 months pregnant at the time. It finally arrived at her house a month after she delivered the baby! 

That's not unusual. Customs can take as long as they want/need to clear a package. Most things go through in a couple of days; however, I've known a few things to take as long as 8 weeks. Delays can occur if the customs paperwork is filled out incomplete, incorrectly or is missing altogether. There can also be a delay if there is a question of whether duty (tax) is owed or even if the item is legal.

Yes. Due to covid19 and just being at customs slows everything down especially if it was already delayed to begin with. 

Yup.  It you  live in, or near Toronto, the mail will have to clear Customs in Mississauga, which is the Black Hole of Canada Post. Packages go there to die.  It takes a long time to clear there.