very interesting theory.
Although I haven't come across many Kannadigas who choose en_CA due to KA and CA sounding similar, this is an angle for sure.
But OP's guess (en_CA alphabetically above en_GB / en_US) is a more possible reality.
Another trivia: Kannada-English dialect is called "Kanglish" here. Ex: "ಲಾಕ್-ಡವ್ನ್ ! ಬಸ್ಸು ಕಾರು ಎಲ್ಲಾ ರೋಡಿಂದಾ ಬ್ಯಾನ್!" [phonetic: 'lockdown! baSSu, kaaru ellaa road-indaa byaan!'] Though the sentence is accepted to be Kannada, only true Kannada word there is "ellaa" (=> all)
Kanglish is the norm here, and textbook Kannada isn't getting good love from many. The onslaught of Sankrit on pure classical Kannada is a different topic altogether, for another day!
*people from Karnataka who speak Kannada.