This is how you would answer the questions in the "Am I Canadian" tool:
Where were you born? Outside Canada
Crown servant? No
Naturalized? No
One of my parents was: (several choices, incuding Born in Canada?) No
I was: Born between 1947 and 1977
How did parent become Canadian? Born outside Canada to a Canadian parent
Which applies to parents' citizenship? Neither applied for citizenship*
Was your birth registered? No
You are probably not a Canadian citizen
*Under the 1946 Citizenship Act, the foreign-born child (your mother) of a Canadian-born father (your grandfather) would have become a Canadian citizen on January 1, 1947 if they were 1) admitted to live in Canada as a permanent resident at that time, or 2) a minor. Your mother was probably not living in Canada in 1947 if you were born in the USA in 1948, and she was not a minor. Therefore, she probably did not become a Canadian citizen until she was made one under the 2009 changes to the Citizenship Act. Her status when she was living in Canada before 1947 was British subject (as the daughter of a British subject father). If you were looking for a record of the Canadian citizenship of your mother when she was living in Canada before 1947, you wouldn't find one, because Canadian citizenship didn't exist until 1947.