A reader writes:

I have a query for you which i have been pondering for a while.

"Are all those who are in Heaven.. Saints? Then what is the difference between Saints canonized by Catholic Church and all "other Saints"

Thanks.

Yep.  All in heaven are saints.  In fact, Paul calls all believers saints (holy ones).  That's why we have the Feast of All Saints, to celebrate all the uncounted and uncanonized saints who make up the bulk of the heavenly host. 

Curiously, to be "holy" (set apart) is not necessarily to be saved in the ultimate sense of "going to heaven".  Hitler, for instance, was made holy (set apart) when he was baptised.  It does not therefore follow that Hitler led a "saintly" life.  John warns his community that apostasy is a real possibility:

Children, it is the last hour; and as you have heard that antichrist is coming, so now many antichrists have come; therefore we know that it is the last hour. They went out from us, but they were not of us; for if they had been of us, they would have continued with us; but they went out, that it might be plain that they all are not of us. (1 John 2:18-19).

And in this, he is simply following his Master, who likewise warns the one he makes holy that the salt can lose its savor and that that

If a man does not abide in me, he is cast forth as a branch and withers; and the branches are gathered, thrown into the fire and burned. (John 15:6)

Catholics therefore do not believe in a "once saved, always saved" gospel, nor in the notion of "the eternal security of the believer".  They believe in cooperation with grace, not in magic.  As Jesus and Paul teach, that we are "called to be saints" (as Paul puts it) but this requires our developing habits of obedience to Jesus and persistent virtue with the help of the Holy Spirit.  These things, pursued till we are fully conformed to the image of God in Christ, are what make people saints in the sense of "dwellers forever in heaven".  So we were saved (by Christ through his death and resurrection); we are being saved (by his ongoing work through the sacraments and our cooperation with grace); and we will be saved (when we pass this probationary period, die in a state of grace, and are safely in heaven (or purgatory, which finishes the job of readying us for heaven if we did not finish it here).

When the Church “canonizes” saints she is holding them up as sterling public examples of what it means to be a disciple of Jesus Christ.  A “canon” is a ruler or yardstick.  The idea is not “These are the only people in heaven” but rather “This person is a reliable yardstick for measuring what a healthy disciple of Jesus looks like.” 

It is notable that many saints are, paradoxically, not healthy.  Paul, for instance, was literally unhealthy, having some “thorn in the flesh” with which he struggled:

[T]o keep me from being too elated by the abundance of revelations, a thorn was given me in the flesh, a messenger of Satan, to harass me, to keep me from being too elated. 8 Three times I besought the Lord about this, that it should leave me; but he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." I will all the more gladly boast of my weaknesses, that the power of Christ may rest upon me. (1 Cor 12:7-9).

Others, such as St. Benedict Joseph Labre, have been afflicted with mental illness such as schizophrenia.  Still others, like St. Jerome, had terrible tempers.  The saints are heirs to all the deformities and problems that body, mind and soul can be heir to.  This does not make them hypocrites, it makes them people who persistently and faithfully brought whatever hand life had dealt them to God and asked for his help in changing and offered what they had in love to God and neighbor.  I find the crabby saints a great help since they give me hope that a jerk like me can be saved too.