Hi, Posting a bit more information if known - will help others help you -
Your Great Grandparents - were Peter and Catherine FRANK -to USA in 1879
What was your GGrandmothers maiden name?
Peter FRANK died in 1901 USA -
Citizenship Records - from the state where application was made or National archive in Washington DC
Registration of Death - depending on requirements of the time may show personal information -
What were the names of the FRANK children who came to Canada - When
Canadian Naturalization.
Obituaries - Registrations of Death - Marriage etc
Search 1916 - 1921 [ last available ] Census for names of family members
Following up on the names of the children -
Local History Books
Family may have submitted family history/ stories to a Local History Book Project in the mid to late 1980's
Saskatchewan Vital Events Index - Online : An ongoing process - far from complete - No marriages available
http://genealogy.ehealthsask.ca/vsgs_srch.aspxShows 18 FRANK Deaths 19 FRANK Births.
Did the entire family - remain in Saskatchewan ?
Many persons moved during the 1930's