I haven't done much work with IIIF Presentation API 3.0 yet, so the following should be read with caveats.

A IIIF Presentation API 3.0 manifest is a JSON-LD document structured:

• Manifest
  • Items
    • Canvas(es)
      *Annotation Page
      *Annotation(s)
  • Range
    • Canvas(es)
      *Annotation Page
      *Annotation(s)

There are no Sequences.

Canvases have content painted onto them via Annotations collected in Annotation Pages, but, there is no longer a special class of Image annotation. All content -- Images, Text, Video, Audio, etc -- is associated with a canvas in the same way.

In addition, Annotations can be collected together in an Annotation Collection.

Annotation Page

{
  "@context": [
    "http://www.w3.org/ns/anno.jsonld",
    "http://iiif.io/api/presentation/3/context.json"
  ],
  "id": "https://example.org/iiif/book1/annopage/p1",
  "type": "AnnotationPage",

  "items": [
    {
      "id": "https://example.org/iiif/book1/annopage/p1/a1",
      "type": "Annotation"
      // ...
    },
    {
      "id": "https://example.org/iiif/book1/annopage/p1/a2",
      "type": "Annotation"
      // ...
    }
  ]
}

Annotation

IIIF Image Annotation with painting motivation.

{
  "@context": [
    "http://www.w3.org/ns/anno.jsonld",
    "http://iiif.io/api/presentation/3/context.json"
  ],
  "id": "https://example.org/iiif/book1/annotation/p0001-image",
  "type": "Annotation",
  "motivation": "painting",
  "body": {
    "id": "https://example.org/iiif/book1/res/page1.jpg",
    "type": "Image",
    "label": {"en": ["Page 1"], "es": ["Página 1"]},
    "format": "image/jpeg",
    "service": [
      {
        "id": "https://example.org/images/book1-page1",
        "type": "ImageService3",
        "profile": "level2"
      }
    ],
    "height": 2000,
    "width": 1500
  },
  "target": "https://example.org/iiif/book1/canvas/p1"
}

There's an Annex document explaining how you can use IIIF Image API services:

http://iiif.io/api/annex/openannotation/#iiif-image-api-selector