I actually did this awhile ago - end of May or else June 2007. I emailed Transport Canada with a bunch of questions and comments back then. :thumbsup:
The laws in Canada allow for carseat manufacturers to certify their seats up to 48lbs rf'ing right now - but nobody has ever done it. It's ultimately up to the manufacturers to make & certify seats to higher rf'ing weights, so maybe with enough people pestering them more manufacturers will give it serious thought.
If I was to pick one manufacturer as the most likely to figure out a way to test to higher weights, I'd probably go with SK and the Radian - with it's steel frame I think it's most likely to pass with a higher weight dummy without any major modifications to it - though perhaps a 2nd rf'ing boot would be needed to reduce the recline?
I imagine if Britax put a rebound bar on it's convertibles, and then required australian style tethering they'd also be able to pass rf'ing at higher weights without having a foot prop - which from what I've gathered is one of the big problems as it's not allowed in the US (not sure about Canada...) And then that (rebound bar, australian tethering,) would need to be combined with having a dummy that would fit appropriately in the seat in order for testing. I guess that is where the government would be able to help - having another AMD added would probably be necessary...
eta: Now that I think about it, I've corresponded with Evenflo about the rf'ing weight limit on the EFTA in Canada. Though unfortunately I didn't get anywhere, they said they'd look into it and discuss it with TC. Who knows if they have or not though, that kind of thing tends to move at a snails pace. *shrug*