[0] https://www.flyradius.com/bombardier-q400/fuel-burn-consumpt...
[1] https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085...
Flightaware puts the actual distance at 760km, so it'd be ~844kg of CO².
I found this great guide by the David Suzuki Foundation which assesses different carbon offset vendors with a few different measures:
https://davidsuzuki.org/wp-content/uploads/2019/10/purchasin...
Pages 42-49 go into the different criteria, Page 50 is the table scoring them all.
I decided to go with https://carbonzero.ca, it was $19.89CAD for 0.88t. Thank you for your help :)
[0] https://www.flyradius.com/bombardier-q400/fuel-burn-consumpt...
[1] https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085...