I'm not sure how this "buy first, decide what you need later" thing is supposed to work.
All heating systems start with a room-by-room, zone by zone heat load calculation, and from there you can decide what's appropriate.
Multi-zoned systems using ducted air delivery come with some inherent inefficiencies. If you're splitting the space up into two 750' units the heat loads of any single unit will be a tiny fraction of the output of the Rheem, and there is no way this place need 2.5 tons of cooling.
Start with the gross heat load calc. Assuming it's a rectangle with 2x4 walls and 2x12 attic & floor joists you have about 1500' of gross wall surface. Assuming a 15% window & door/floor ratio you're looking at about 225' of that as window and door area. For yuks I'm going to assume you have R40 in the attic (code-min for new construction is now R50.
The 99% outside design temp for Ottawa is -22C/-8F and lets assume a 20C/68F interior temp, for a 42C/76F delta-T at design condition.
The U-factor for insulated 2x4s is about 0.1 BTU/degree-F foot, and you have about (1500-225=) 1275' of wall area. At a delta-T of 76F and U-factor of 0.1 your heat loss from walls is about (0.1 x 76F x 1275=) 9690 BTU/hr.
Assuming you have low performance double-panes and 2" solid doors you're looking at about U0.5 for the windows & doors. So the window & door losses are (0.5 x 76F x 225=) 8550 BTU/hr
Assuming a 10% framing fraction on the attic floor joists and R38-R40 insulation the U-factor on the ceiling will run in the neighborhood of 0.03 BTU/ degree-foot, so the ceiling losses are around (0.03 x 76F x 1500' =) 3420 BTU/hr. If it's only crappy R19s twice that, so let's call it 2 x 3420 =6840 BTU/hr.
Add it all up and it's still only 9690 + 8550 + 6840 = 25,030 BTU/hr for the whole house.
Give it a hefty 30% allowance for floor losses and air leakage and you're still at only 33,000 BTU/hr, only about half the output of that furnace, and that's for the whole place. And that's before deducting for interior heat sources like hot-bodies and the 24/7 plug loads like refrigerators, etc. Odds are pretty good that the true whole house load is in the 30K range, which would put it at about 15,000 BTU/hr per apartment for heating loads. Cooling loads are likely to be under 1-ton per apartment (unless one has all the windows facing west with no trees or buildings blocking the afternoon sun.)
Seriously, use a spreadsheet with room-by-room wall/window/door/ceiling dimensions to come up with room by room subtotals, and then the apartment by apartment subtotals. If your walls & windows are different from described tell me what they are and we can come up with more appropriate U-factors. With a reasonable heat load calc to start with it's easier to figure out what the appropriate solutions are, but it's probably not going to be the equipment you have in hand. (Can you return or exchange it?)