If your aircraft is certified under Part 23 as opposed to CAR3, it would be obligated to abide by the following:
§23.1441 Oxygen equipment and supply.
(a) If certification with supplemental oxygen equipment is requested, or the airplane is approved for operations at or above altitudes where oxygen is required to be used by the operating rules, oxygen equipment must be provided that meets the requirements of this section and §§23.1443 through 23.1449. Portable oxygen equipment may be used to meet the requirements of this part if the portable equipment is shown to comply with the applicable requirements, is identified in the airplane type design, and its stowage provisions are found to be in compliance with the requirements of §23.561
I added the boldness to the text.
So, what portable oxygen is identified in an aircraft's type design? What is a "type design" anyway?
One source says Type design is this:
(1) The drawings and specifications, and a listing of those drawings and specifications, necessary to define the configuration and the design features of the product shown to comply with the requirements applicable to the product;
(2) Information on dimensions, materials, and processes necessary to define the structural strength of the product; and
(3) The Airworthiness Limitations section of the ICA as required by Parts 23, 25, 27, 29, 33, and 35, or as otherwise required by the Administrator
So how do you get from needing it to be identified in the type design to its ok to use it? Unless you find where it is identified... you can't connect them.
But CAR3 was more lenient on this and portable oxygen systems do not violate it. I find no mention of Oxygen requirements in CAR3.