Does a basement apartment in Ottawa need two layers of Type X?

No, Ontario's Building Code does not require two layers of 5/8-inch (15.9 mm) Type X drywall between a basement apartment and the main dwelling. The Code gives two routes, and a single layer of 5/8-inch Type X on the right surfaces is one of them.

What the Code actually says

Ontario's Building Code (9.10.9.16) sets out the separation between dwelling units in a house that has a secondary suite. The first route is a fire separation with a 45-minute rating (9.10.9.16.(1)). The second route is a continuous smoke-tight barrier of not less than 5/8-inch (15.9 mm) Type X gypsum board installed on both sides of the walls between the units and on the underside of the floor-ceiling framing above the suite (9.10.9.16.(4)). Where the house is sprinklered throughout, 9.10.9.16.(5) waives the Type X barrier route; ask the City how that applies to your house. Light-frame walls, columns, arches and beams that carry the floor between the units also need not less than 5/8-inch Type X protection (9.10.8.3.(2)).

These are minimums for new work. The City of Ottawa decides through the permit which route applies to your renovation, and you should ask them directly how the clauses apply to your specific house.

For an existing house, the Code's Part 11 compliance alternative C156 accepts a 15-minute horizontal fire separation where smoke alarms are installed in every dwelling unit and common area and are interconnected. The Code text does not name which assembly gives 15 minutes; ask the City. A building permit is required before proceeding with a secondary suite, even where limited work is proposed, because the change of use must be reviewed; the drawings must show the wall and floor-ceiling construction between the new unit and the main dwelling.

One more thing worth knowing: the barrier must be continuous (9.10.9.2), so openings in the ceiling, such as pot lights or duct penetrations, are part of the conversation with the City and the contractor.

Sound between dwelling units is a separate Code matter; ottawasoundproofing.com covers that.

When you have two written quotes in front of you, set them side by side and check that each one names the board thickness and type, states exactly what is removed and what goes back, and says plainly whether primer and paint are included or are extra.