The rf limit on the MA in Canada is 30lbs, a lot of sites just copy & paste descriptions from the main manufacturers page not taking into account the difference between countries.
As for age, most kids will fit to age 4.5 to 5, some as long as age 7. (talking ff'ing here.)
Some kids will outgrow it younger though, it just really depends on the child.
It does have some of the highest slots available in Canadian seats right now though, but some kids do end up needing the Radian to get to 40lbs. Both the Radian and the Triumph Advance give more growing room height wise, with the Radian providing the most.
When the Nautilus and Frontier eventually show up in Canada, they should both allow more height room than even the radian, but they will also be ff'ing/booster combination seats and not have the option to be used rf'ing. There's also the new true fit that will be coming out sometime in the next few months, how it'll fit kids IRL in comparison to the other seats I can't speak of right now. I'll be able to answer that question once it's available locally though.