It seems odd that Patrick, Ted and Stevie keep calling Johnny and Moira "Mr. and Mrs. Rose". Is that a Canadian thing?

I finally watched Schitt's Creek now that it's become available on Netflix in my country and love the show!

I keep noticing that the "young" characters like Patrick, Ted, Stevie, and Twyla refer to Johnny and Moira as Mr./Mrs. Rose throughout the entire show -in case of Patrick even after he and David got married. Is this common in Canada? I'm from Germany and our culture always struck me as much more formal in that respect (at least compared to the US), but growing up even for me it wasn't unusual to call even my friend's parents by their first name. Calling your spouses parents by their last name would be extremely unusual and it seems rude and unwelcoming if your in-laws didn't offer to switch to a first name basis.

Edit:

For clarification since it comes up in a lot of comments and I think I explained it poorly: in Germany it's considered normal and polite for children and adults to adress a friend's parents as Mr/Mrs unless you're told otherwise. But it's not unusual to be offered to use first names instead.

However, if I were to meet my friend's or partner's parents for the first time as an adult, I would also expect them to adress me by my last name. It's traditional and polite to let the older person decide on the formality level, but between adults, it's usually understood that it goes both ways. If an older adult calls me by my first name or uses the informal "du", that's an unspoken invitation to do the same.

In case of Stevie, she and Johnny are also equal business partners and the Mr. Rose/Stevie dynamic they have feels a bit condescending to me since it implies she's in a junior position.