After root canal on canine tooth #11, iam curious to know what are the symptoms/how it feels if the drill touches or drills into the sinus cavity floor?

Depends: You might not have any symptoms. That being said a sinus infection , pain in the tooth root tip area and sinus pain are some of the symptoms you could have. You might want to go back to the dentist and have a radiograph taken of the area usually its unlikely a canine tooth will result in a sinus perfortion.

Almost impossible: I have never heard of any case where a dentist has drilled into the sinus when performing a root canal therapy. That would be quite remarkable and extremely unlikely. If is more likely to occur during the removal of posterior root tips during extractions or during the placement of dental implant fixtures. In any case, bleeding from the nose or seeing blood when sneezing could be one symptom.

Not going to happen: The root of tooth #11 lies under the floor of the nose and not in the sinus cavity. You should be numb with local anesthetic so you will feel pressure , but should not feel pain. I have never seen or heard of drilling into the sinus thru the six front teeth under the nose.