You are not legally required to inform current or prospective employers about your medical condition. If MS is affecting your ability to do your job, you only need to describe limitations you’re experiencing that are relevant to your job. Your employer is generally required to provide any necessary accommodations you need to help you perform your job. You have the right to confidentiality at work regarding your medical information and MS diagnosis. If you choose to tell your employer about your diagnosis, be self-assured and non-defensive.
For more information from the MS Society of Canada about MS and employment, visit http://mssociety.ca/en/pdf/EmploymentIncomeSupport_EN.pdf
You can also visit The Canadian Abilities Foundation @ http://www.abilities.ca for information and inspiration.