Is there anyone in heaven? (Catholicism) In Catholicism people pray to the saints, angels and the Virgin Mary. Is then, in Catholicism, heaven filled, besides angels, with the saints and the Virgin Mother?
Yes, there are people in heaven.

Some, who were born before Christ's resurrection are:


Elijah



  2 Kings 2:1-12
  “And it came to pass, when the Lord would take up Elijah into heaven by a whirlwind…And fifty men of the sons of the prophets went, and stood to view afar off: and they two stood by Jordan….And it came to pass, as they still went on, and talked, that, behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven….And Elisha saw it, and he cried, My father, my father, the chariot of Israel, and the horsemen thereof. And he saw him no more…”



Enoch



  Hebrews 11:5
  “By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God.”



The Blessed Virgin Mary



  CCC 966
  "Finally the Immaculate Virgin, preserved free from all stain of original sin, when the course of her earthly life was finished, was taken up body and soul into heavenly glory, and exalted by the Lord as Queen over all things, so that she might be the more fully conformed to her Son, the Lord of lords and conqueror of sin and death."508 The Assumption of the Blessed Virgin is a singular participation in her Son's Resurrection and an anticipation of the resurrection of other Christians...


And probably many others.

It is a point of mild contention whether canonisation is infallible, but most theologians agree that a papal canonisation is infallible. 
Most notably St Thomas Aquinas (Quodlib. IX, a. 16): 


  Since the honor we pay the saints is in a certain sense a profession of faith, i.e., a belief in the glory of the saints, we must piously believe that in this matter also the judgment of the Church is not liable to error.


So, I would say Heaven is 'full' (although it is an immaterial place) of saints. Although not as full as Hell.

Here are some helpful resources.
http://www.newadvent.org/cathen/02364b.htm - Infallibility section
https://taylormarshall.com/2008/08/is-assumption-of-mary-in-bible.html
https://www.catholic.com/qa/are-canonizations-infallible