You're right. I don't remember seeing these kind of deals. It's still $399 here in Canada.
Regardless, PS4 was more expensive throughout its lifetime, and for the majority of 2015.
The PS4 was released at a time where the CAN$ was at parity with the US$ and it’s original was 399,99$ like you said. It saw an increase at 450$ latter on once the CAN$ value started to drop and returned at 399$ with it’s first permanent cut in 2015. The Switch was at 399$ for the majority of it’s life and dropped recently to 379$ to adjust to $ value.
But overall, both consoles are sold in the same price range in Canada and it doesn’t seem to affect the sales of each ones.