Here are
common measurements for carseats, they are not all available in Canada and some are not even on there.
As for the seat with the highest slot, that would be the
Radian (Canadian Tire, $199) at 18". My friend just got a
Radian (at Canadian Tire by Polo Park, they had 5 instock) and I was surprised at how much room her 3yr old has in it! She has a good 3-4" left before she outgrows this seat by height. We installed the
Radian in the parking lot (we live in southern MB) and it was pretty easy to install using
LATCH (didn't try a seatbelt install). The
Radian goes to 48lbs in Canada and 65lbs in the US, so if and when Transport Canada redefines the definition of a child and increases that weight, then the
Radian will go to 65lbs in Canada as well.