Received phone call. Did not answer.

Got a text message from 613-536-4132 to confirm employment for someone named Christina and to call back 1 866-950-7227.  I tried to call back and got a message that the number cannot be reached from my calling area (California, USA)

Your message was from Service Canada, Canada's Federal government employment agency that, among other things, is directly responsible for Employment Insurance and Canada Pension Retirement Pension.
http://www.servicecanada.gc.ca/eng/home.shtml
It's likely that your number was given to them by somebody who had completed their forms. It is important and helpful to answer their calls. They have a toll free number available for the US.
From their website:
"From within Canada and the United States, you can call us toll-free Monday to Friday. For callers in Canada, service is available from 8:00 a.m. to 8:00 p.m., your local time. From the United States, service is available from 8:00 a.m. to 8:00 p.m. Eastern time. Service is provided in English and French.

Toll-Free: 1 800 O-Canada (1 800 622-6232)"