That is quite a special feather.
Is it fairly newly emerged, or been there several years?
If it does not irritate him, I wouldn't worry about it. Being of odd position and conformation, however, it could be prone to injury with normal activity.
Have you removed a feather before?
If it bothers him or becomes injured: gently restrain him in a thin washcloth, do not compress the chest. Grasp the feather at the base near the skin, and pull firmly but slowly (don't "jerk"). Hemostats or even tweezers may help, and generally it is a 2-person job. A "root" should be on the feather after you pull it out. Mature feathers should not bleed after removal, but it can be a painful process.
I notice that his feet look abnormal, appearing to be hyperkeratotic. This is common in canaries and is a combination of genetics and nutrition, and sometimes subcutaneous parasites. With an abnormal feather, I would strongly urge that his nutrition be improved (see guidelines below) and that you set up a routine well-check with a bird-experienced vet. Canaries live a long time and it is well worth it.
Pet/feed store medications and home remedies are harmful, ineffective, immuno-suppressive, and make them much worse and may interfere with the veterinarian's diagnosis and treatment. Do not use them. Homeopathy and natureopathic techniques do not work in avians and can actually be very dangerous.
I know it is expensive, but you may not have many home options, because the first thing you need a vet for is to find out what is going on. Treatment is only as good as the diagnosis. If you call around, you may find a vet to work within your means.
I really must stress that you need a bird-experienced person, and not just a vet who advertises that they care for birds.
You need to take your bird to see an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check
https://aav.site-ym.com/?page=basiccare click on "find a vet"
Feather issues can be caused by a multitude of things, including bacterial skin infection, viruses, fungal infections, allergies, metal poisoning, hormonal flux, psychological or combination of these factors. The difficulty is diagnosing the problems and assigning an intelligent treatment plan. Your vet will want to run a number of tests so that appropriate medications can be prescribed.
Inflammatory skin/follicle disease is common. The causes can include local infection, metabolic problems, or even intestinal parasites. It can also be a prime area for even more serious problems like skin cancer. An avian-experienced vet should take a look at the poor bird, and run some tests.
If this were my patient, and money no object, I would start with complete fecal analysis and direct smear, stained with Sedi-stain and unstained for multiple parasites, fungi, spirals; direct smear stained with Sedi-stain and unstained of the oral cavity and feather pulp; bacterial culture and sensitivity of the feather pulp, feces and choana. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. There are MANY DNA/RNA tests for bird diseases. Generally I start them out on medications as indicated by the tests.
Here are a few suggestions that I give everyone: important!
The following guidelines help with basic issues such as nutrition, obesity, good immune status. Surprising how the following can make a bird healthy, and how infrequently birds are ill if they are on the following regimen. No amount of medicine is going to work if the birds' basic needs are not met.
great resource link:
Birds should be on a high-quality, preferably prescription, pelleted diet: I prefer High-potency Harrison's
TOP--canaries generally love this one:
In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc. etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell.
Food and water dishes should be cleaned and changed daily. Keep one set cleaned while the other is in use.
Fresh, perishable food should be placed in separate food bowls. Remove fresh food from the cage after a couple of hours to avoid spoilage.
Change cage papers daily, and clean the grate and tray weekly.
Clean food debris or droppings from toys and perches as needed (which can be as often as once a day).
Grit is not necessary for birds, and will cause digestive problems and death. The best sources of minerals (and vitamins) are leafy greens. Never give grit, gravel sandpaper or cement perches. A bird will eat those to excess when it is not feeling well or if there is a nutritional deficiency. They do not need it at all (an old myth from the poultry days, even poultry do not need it). It can cause an impaction and lead to serious or fatal consequences.