I am a Canadian Citizen in the United States as a non resident alien under an L2 visa (my husband was transferred here with his work) I have an employment authorization card as well as a Social Security Number which says, VALID FOR WORK ONLY WITH DHS AUTHORIZATION, Which I have.
My question is, because I am here temporarily(California), am I except from paying Medicare and Social Security as I will never benefit from it? I am NOT here permanently, we will be moving back to Canada (British Columbia) before the expiration of our visas. If employers have deducted from wages for Medicare and Social Security can this be reimbursed? If any other information from me is required for an answer just let me know!

File a new W4 with the employer.Read it and see if you qualify to check the exempt box. You can get the form on the IRS site.