Formal:
* ಸುಭಾಷಿತ ವಾರ್ಷಿಕೋತ್ಸವದ ಶುಭಾಶಯಗಳು (Subhashita varshikotsava shubhashayagalu): This is a more formal way to say "happy anniversary" and literally translates to "best wishes on the auspicious anniversary".
Informal:
* ಸಂತೋಷದ ವಾರ್ಷಿಕೋತ್ಸವ (Santhoshada varshikotsava): This is a simple and informal way to say "happy anniversary".
* ನಿಮ್ಮ ವಾರ್ಷಿಕೋತ್ಸವಕ್ಕೆ ಶುಭಾಶಯಗಳು (Nimma varshikotsavakke shubhashayagalu): This translates to "happy anniversary to you" and is a slightly more personal way to wish someone a happy anniversary.
Other options:
* ವಾರ್ಷಿಕೋತ್ಸವದ ಶುಭಾಶಯಗಳು (Varshikotsava shubhashayagalu): This is a more general way to say "happy anniversary".
You can also use phrases like "ನಿಮ್ಮ ಪ್ರೀತಿಯ ದಿನಕ್ಕೆ ಶುಭಾಶಯಗಳು" (Nimma preetya dinakke shubhashayagalu) which means "best wishes for your day of love" or "ಇವತ್ತು ನಿಮ್ಮ ಪ್ರೀತಿಯ ದಿನ (Ivatttu nimma preetya dinu) which means "today is your day of love."
Ultimately, the best way to say "happy anniversary" in Kannada depends on your relationship with the person you're talking to and the tone you want to convey.