Can I claim the GST/HST new housing rebate if I buy through a numbered company in Canada?

This answer covers Canadian federal tax law, which applies in every province.

No, a numbered company cannot claim the GST/HST new housing rebate, because only individuals can. Partnerships and corporations are excluded, and an individual also cannot claim if a partnership or corporation co-owns the house. So buying through a company can cost you the rebate you would have had as an individual.

There is an alternative for rental purchases. A corporation that is not a co-op and buys a new residential unit to rent out may claim the new residential rental property rebate on Form GST524 if the purchase was taxable and it is not the builder. That rebate is for units leased or held for lease as residences, and it is not paid where an individual qualifies for the new housing rebate on the same housing. The unit must be self-contained and held for exempt residential rental, and tax must not be recoverable as an input tax credit.

The owner rebate is meant for an individual who will live in the home, or whose relation will, as a primary place of residence. If you are weighing a company purchase, compare both routes with a lawyer or accountant before signing.