They do not contradict each other; there is simply an added layer of competence required for certain buildings.
The Code requires construction to have a designated designer; The Architect's Act/Engineer's Act requires the designer(s) of Part 3 buildings to also be licenced engineers/architects.
Example: I foster kittens for an animal shelter. They are building a new shelter. It is a part 9 D-occupancy building of about 900 square feet (so well below the 300m2 threshold that requires architects/engineers by law). I declared a conflict, and created the plans for the structure. I am the designer (by Code). I am not an architect, and don't need to be.
Under no circumstances can I design Part 3 buildings, because our laws state that Part 3 buildings require engineers and/or architects, and I am neither.
IIRC, Ontario also requires some part 9 buildings to have a certified part 9 designer ...
If you are not an architect, you have just admitted to breaking Ontario law in a public forum. We had someone submit a part 3 design to our office - and they weren't an architect. The individual's plans were sent to the provincial architect's association, who sent a cease-and-desist letter. I believe a $50,000 fine is written into our province's act, but I may be remembering wrong.
If some CBOs accept plans for part 3 buildings from people who are not registered architects and/or engineers, they are exposing themselves to acute liability. The law is
exceptionally clear on this.
Some light reading:
https://www.canlii.org/en/bc/bcca/doc/2021/2021bcca261/2021bcca261.html
If you are not a registered/licenced engineer/architect, you cannot design Part 3 buildings of any kind, nature or occupancy.
This is not complicated.