Adult canine teeth pain out of the blue. No cavities either, any ideas anybody?

Possibly from. Possibly from clenching, grinding, malocclusion, change in medications, stress, etc. Lots of potential causes. Please call your dentist for an evaluation of your occlusion.
Grinding. Could be from grinding. If your tooth has a flat edge instead of point you are grinding on it and that can cause sensitivity and soreness.
Sinus infection. Sinus/nasal mucosal “toothache” is a common heterotopic pain condition. Yes, a sinus infection (sinusitis) or inflammation can cause a toothache, especially in the upper rear teeth and canine. Rec.: see your dentist for definitive diagnosis and treatment.
Three. Bruxism, sinusitis , and the remote possibility that the tooth has become non-vital due to trauma, you will need to have it evaluated locally...