Hi Paige.Sorry for the delay in replying.Yes, more information has recently been found about William Bigsby and Isabella McClellan and their first child, Georgianna, your gggrandmother.Search for recent postings by Susan Crabtree.She's an energetic researcher of your family and has acquired a wealth of knowledge which she's happy to share.
A wealth of Quebec family history data, the Drouin Collection of parish records (which also served as civil records), was recently made available through Ancestry.com (or Ancestry.ca in Canada.)It confirmed the birth of your William Bigsby on May 30, 1841, and his baptism June 20th in Montreal.The records also reveal other family events - the birth ("naissance") of a brother and burial of their father, Thomas Bigsby.I have details, but Susan is the best person to keep you informed of this and future discoveries.
I'd long argued that Georgianna must have been born in the village of Queens, now part of London, Ontario, and not in a similarly-named area of New Brunswick as an LDS researcher had guessed.Her census data shows her born in what is now Ontario (then called "Upper Canada" or "Canada West".)It now appears that William's widowed mother Hannah (née Smith) moved to the vicinity of London, Ont., and remarried. That, plus London's proximity to Michigan where William & Isabella were married, suggests they were visiting his mother when the baby was born.