Would you think of a Britax Frontier? I know they are pricey but with another one behind this little one, you will have a fair bit of time in an expensive carseat. (I think they are $299 in Canada.)
I have a 6 year old who is maybe 42lbs. and maybe 42inches in a Britax Frontier (and her 4 year old brother, same weight, slightly shorter as well). I like the seat.
I never had an issue installing it (except latch).
At 40lbs and 5 years, and in Canada (not sure which province) but you likely will be boostering for awhile - so a 5point isn't that unusual. I wouldn't do a booster unless it made no sense to buy another high weight 5-point.
Not sure if an Apex converts to a booster or not - but that is one way a Frontier 'doubles up'.
My opinion of course!