The 3-in-1 only harnesses to 40 pounds; after that it must be used as a belt positioning booster.
The 3-in-1 has very low top harness slots, so most kids won't even make it to 40 pounds before getting too tall for the harness. The top harness slot position is the second-to-top headrest position. The top headrest position is only to raise the headrest higher in booster mode. Therefore, the top useable harness slot position is very low. Once the child's shoulders go over that slot, they are too tall for the harness and have outgrown the harnessed mode of that seat. Since kids MUST be harnessed to at least 40 pounds in Canada, another harnessed seat with taller top harness slots and possibly a higher harnessed weight limit will be needed before the child can move to a belt positioning booster.
The 3-in-1 in booster mode will not last as long as a dedicated booster, nor will it provide the side impact protection that some dedicated boosters (like the Graco Turbo Booster and Britax Parkway, both of which have EPS foam headwings and adjust tall enough to accommodate most kids to 5 feet tall).
My dd outgrew the 3-in-1 by height at just 2.5 years old and 33 pounds. We then had to find another harnessed seat with taller top slots or switch her prematurely to booster mode (NO WAY).
In Canada, a better choice for a convertible seat would be the Cosco Touriva/Scenera or the Safety 1st ComfortRide (same as Touriva but with more padding). These will still probably be outgrown by height before 40 pounds, but the top slots are a smidge taller than the 3-in-1's top slots and they are much more affordable.
Once the convertible seat is outgrown, good combination seats to consider are the Graco Ultra/Platinum CarGo (NOT the Treasured CarGo or MyCarGo; these do not have a front harness adjuster) and the Evenflo Express/Vision/Chase. The CarGo harnesses to 48 pounds, the Evenflos to 47 pounds (only in Canada, because top-tethering seats is required; in the US, where top-tethering is not required, these seats only harness to 40 pounds). Both the CarGos and Evenflos have top harness slots at least two inches taller than the 3-in-1. Both turn into belt positioning boosters once the child has outgrown the harness, but the belt positioners on combination seats sometimes do not work well with all vehicle seatbelts. Sometimes a dedicated booster (like the Parkway or Turbo) is a better fit for the vehicle, belts and child.
HTH!