Is the anime of "Tokyo Ghoul:re" (season 3) canon?
Yes, Tokyo Ghoul:re is canon

If you take a look in the wiki you can see that Tokyo Ghoul:re (東京喰種トーキョーグール:re, Tōkyō Gūru:re) is a sequel to the Japanese manga series Tokyo Ghoul written and illustrated by Sui Ishida. 

And yes, Tokyo Ghoul:re picked up 2 years after the events that ended Tokyo Ghoul