According to http://www.legislationline.org/?jid=11&less=false&tid=102 and http://www.hrsdc.gc.ca/en/lp/spila/wlb/wfp/11Maternity_Leave.shtml they can not fire your for getting pregnant. If they do, I guess you would start by calling Service Canada and find out from them who you should talk to. You are entitled to EI while you are on maternity leave and your employer normally has to keep your job for you. However, since you are on contract, if your contract is up during the time that you are on maternity leave, I am not sure what will happen.