Can a Canthoplasty Be Reversed?

When was your surgery and for what reason?
Had you had previous blepharoplasty surgery that developed complications?
Waiting is your best bet as many structures loosen with time. Canthoplasty is designed to enhance lower lid support and decrease the risk of exposure to your cornea, etc. It typically doesn't have any effect on position of the upper lid unless your surgeon purposely creates scar to narrow the outer corner of your eye. You were used to seeing a big open eye because of the looseness of the lower lid. Tightening created a smaller opening, but enhanced function of and protection by the eyelid. You must have been having complications that necessitated lid repair like dry eyes, excess tearing, corneal exposure, etc. I agree with Dr. Seckel with regards to a reversal of course being the wrong way to go.
Fat grafting to the upper lid can be used to fill out hollow upper lids and is an alternative to brow elevation procedures. I doubt you want to lower your brow as your eyes will look even smaller.
Know your goals before embarking on such complex revision surgery.
In my opinion, one of the best blepharoplasty surgeons in Australia is Bryan Mendelson. Dr. Steinsapir also provides a list of oculoplastic surgeons that may work for you.

Lowering of the brows and buccal fat transfer may in fact cause your eyelids to appear even smaller. Since your stated concern was that your eyes now look smaller, I would avoid this. Patients generally have their brows elevated to make their eyes appear wider or more open rather than lowering the brow.

Dear Anna
Be very careful what fixes you seek out to fix your issues. In particular, yes buccal fat can be used to graft into the upper eyelids like any fat material. However, removal of the buccal fat will alter your facial appearance. When fixing a problem, I think it is very important not to cause a new problem. There is no evidence that there is any thing inherently special about the buccal fat. If you are going to have fat placed, there are many other sites it can be harvested from without changing the facial appearance.
Canthoplasty can easily be revised if one routinely performs canthoplasty. The problem is that general plastic surgeons and facial plastic surgeons do not routinely perform this surgery, they are not comfortable with it and this is reflected in the quality of results that are seen when they attempt this approach. The problem is that the cathoplasty is a very powerful surgery but also very unforgiving. It requires a great deal of experience to have finesse with this surgery. Only eye plastic surgeons have enough experience with this procedure to obtain the level of control you will need to have an improved outcome, and even then only certain eye plastic surgeons.
In Australia, you have some excellent eye plastic surgeons. Consider having a consultation with any of the following surgeons: Timothy Sullivan, Brisbane; Ian Francis, Chatswood; or Allan McNab, Victoria.