Are common law spouses eligible for benefits of deceased veterans?

"VA will recognize a common law marriage if the state in which the Veteran resides recognizes common law marriage, and the state's requirements for a common law marriage are met. ... The Veteran need not submit evidence of the already-recognized marriage with an application for a new benefit."

Make an appointment with your VA dept in your County and talk to a representative.

In Canada yes.

If you are in the US you will have to talk to Veterans Affairs.