Please list the top 3 cities with the most number of tweets posted in Canada.
"Canada" is the Country; city with most number of tweets refers to City where Max(Count(TweetID))
SELECT T.City FROM ( SELECT T2.City, COUNT(T1.TweetID) AS num FROM twitter AS T1 INNER JOIN location AS T2 ON T1.LocationID = T2.LocationID WHERE T2.Country = 'Canada' GROUP BY T2.City ) T ORDER BY T.num DESC LIMIT 3