Since you are a vet tech...you might be able to pull this off.
This is a strange one....if it is advanced canker then usually the parents would have stopped feeding....but you say the crop is full...which is unusual.
Here's the dicey part: You wanna medicate with Metronidazole or Ronidazole. BUT...you cannot give it orally because the crop is static (unless it is regurgitated food you are seeing). Also, for stasis you wanna syringe feed some stuff...but again, if the crop is static, that also becomes very dangerous to try.
1) are you sure the crop is full ? if so...this makes things complicated. If it is full, in some instances you'd need to go into the crop with a feeding tube and try to gently siphon some of the food out. Because you cannot put anything else in there and expect it to move thru/absorb. If you try, regurgitation or aspiration might occur.
BUT...intubating a canker bird can likely shear off the canker growths in the throat, and that will kill the baby really fast.....so any sign of canker growths nixes intubating.
IF THERE IS PHLEGM...you CAN try to clear out as much of that as possible so baby can at least breath more easily. But again, don't stick anything down the throat, just clear any phlegm from the mouth and make sure you don't accidentally dislodge anything SOLID.
2) Crop stasis steps are usually:
a) get the baby very warm....ambient temperature of 85 degrees F...so a brooder, incubator is optimal. If not, go with a heating pad under a layer of towel set on low, and cover the entire carrier/cage/enclosure to keep the heat in.
b) gently massage the crop for a few minutes at a time. Then stop for 10 minutes, then repeat for another few minutes. Do maybe 3-4 cycles of this.
c) once the baby is warm and the crop massaged, see if there are any signs of it emptying. If there are signs it is moving....
d) start the canker med., and ....
e) give him/her a few drops of Apple Cider Vinegar mixed w/ water (1 tablespoon per 8 ounces) ...OR...straight applesauce.
Massage the crop again after a few minutes of ingesting. The ACV/applesauce attempts to correct the pH imbalance of the sour crop.
IF you agree it appears to be canker, then you have to go to steps 2) and forget siphoning the crop...and you and the rest of us will then pray a little that the crop can get moving sufficiently, before the baby dies from the canker.
NOW, if your facility has the ability of delivering a canker med INTRAVENEOUSLY (a shot into the chest/breast area)....have them do it. Metronidazole, Ronidazole, or CARNIDAZOLE would all work on canker. That would be quite awesome, because these meds start to work really fast, and if we can get the canker to subside, it'd be easier to address the crop stasis (IF it is static). 5mg given twice daily, for at least 7-10 days.... is a typical dosage for Metro or Ronidazole.
Both are very flexible in that overdosing does not seem possible with the '-Zole' drugs, as I have known folks who administer 25mg daily with no adverse effects.
For Carnidazole, 5mg once a day for 3 straight days then stop.
Keep us posted. Thanks for saving your pal.