I moved to Canada from the US when I was pregnant with DS. My parents bought us a very nice travel system (infant carseat/stroller) from the US and brought it to us as a baby shower gift, and we were using it several months before I even found out the there is a car seat restriction here. I continued using the carseat until DS outgrew it. I have seen the exact same system here in Canada (for about 100 bucks more) and I'm not about to waste a perfectly good, safe carseat and stroller just because it doesn't have a stamp.
Nobody has ever batted an eye at our seat or stroller in the almost year and a half we used them. That covers multiple border crossings, flights, and general zipping all over the place.
And agree with PPs, the restriction seems to only be on carseats, not strollers.