I'm not sure about equality law in Canada, but in England, the use of a comparator is key.
If a female model in the uk was making a claim of sex discrimination, she would claim that she is being treated less favourably than male models. I expect both male and female models are required to wear whatever the client wants modelling. The client will also select their models based on how they look, and the agency will be sent a brief stating what they want 'supplied'. What the clients want is not down to the agency, and the agency's role, if they accept the job, is to select which models to send. It's difficult to think that sex discrimination would arise here, other than linked to terms and conditions.
When it comes to gender reassignment discrimination, I expect the above would apply. The agency would select models to supply to a given job in line with their look matching the brief. If a job required the agency to supply someone with the trans model's looks and chose someone else with these looks, over the trans person, because they weren't trans, this would be discrimination. I wonder if this applies to $300000 worth of jobs?!
I think the points about misgendering and being treated respectfully and different to those about work/modelling assignments.